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feat(compiler): Add type inference for MySQL mathematical expressions
Implements recursive type inference for SQL expressions to generate proper nullable types instead of interface{}. Changes: - Add inferExprType() for recursive AST traversal - Add combineMySQLTypes() with MySQL-specific operator rules - Support for division, modulo, and bitwise operators - Proper nullability propagation (NULL op anything = NULL) - Type promotion hierarchy: int -> decimal -> float - Handle MySQL-specific operators (DIV, MOD) Testing: - Add comprehensive unit tests for type inference - Add integration tests demonstrating the fix - All existing tests pass Fixes issue where 'rating / 1024' generated interface{} instead of sql.NullFloat64 for nullable float columns. Database support: - MySQL: Fully implemented - PostgreSQL/SQLite: Conservative fallback (returns nil for safe defaults)
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‎internal/compiler/infer_type.go‎

Lines changed: 234 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,234 @@
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package compiler
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import (
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"github.com/sqlc-dev/sqlc/internal/config"
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"github.com/sqlc-dev/sqlc/internal/sql/ast"
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)
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// inferExprType recursively analyzes SQL expressions to determine their types.
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//
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// It handles:
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// - Column references (resolved from table schema)
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// - Literal constants (intrinsic types)
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// - Binary operations (applies type promotion and operator-specific rules)
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// - Type casts (respects explicit type annotations)
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//
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// Examples:
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//
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// SELECT a1 / 1024 -- infers decimal or float based on operand types
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// SELECT COALESCE(a1 / 1024, 0) -- handles nested expressions recursively
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// SELECT CAST(a1 AS INT) -- respects explicit casts
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//
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// Returns nil if type cannot be inferred, allowing fallback to default behavior.
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func (c *Compiler) inferExprType(node ast.Node, tables []*Table) *Column {
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if node == nil {
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return nil
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}
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switch n := node.(type) {
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case *ast.ColumnRef:
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// Try to resolve the column reference
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// Create a minimal ResTarget for outputColumnRefs
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emptyRes := &ast.ResTarget{}
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cols, err := outputColumnRefs(emptyRes, tables, n)
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if err != nil || len(cols) == 0 {
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return nil
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}
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return cols[0]
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case *ast.A_Const:
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// Infer type from constant value
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switch n.Val.(type) {
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case *ast.String:
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return &Column{DataType: "text", NotNull: true}
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case *ast.Integer:
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return &Column{DataType: "int", NotNull: true}
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case *ast.Float:
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return &Column{DataType: "float", NotNull: true}
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case *ast.Boolean:
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return &Column{DataType: "bool", NotNull: true}
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default:
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return nil
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}
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case *ast.A_Expr:
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// Recursively infer types of left and right operands
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leftCol := c.inferExprType(n.Lexpr, tables)
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rightCol := c.inferExprType(n.Rexpr, tables)
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if leftCol == nil && rightCol == nil {
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return nil
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}
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// Extract operator name
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op := ""
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if n.Name != nil && len(n.Name.Items) > 0 {
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if str, ok := n.Name.Items[0].(*ast.String); ok {
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op = str.Str
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}
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}
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// Apply database-specific type rules
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return c.combineTypes(leftCol, rightCol, op)
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case *ast.TypeCast:
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// If there's an explicit cast, use that type
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if n.TypeName != nil {
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col := toColumn(n.TypeName)
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// Check if the casted value is nullable
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if constant, ok := n.Arg.(*ast.A_Const); ok {
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if _, isNull := constant.Val.(*ast.Null); isNull {
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col.NotNull = false
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}
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}
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return col
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}
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}
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return nil
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}
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// combineTypes determines the result type of a binary operation.
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// The logic is database-specific and handles operator semantics for each engine.
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func (c *Compiler) combineTypes(left, right *Column, operator string) *Column {
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// If either operand is unknown, we can't infer the type
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if left == nil && right == nil {
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return nil
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}
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// If one operand is known, use it as a hint
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if left == nil {
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return right
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}
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if right == nil {
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return left
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}
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// Result is nullable if any operand is nullable (SQL NULL propagation rule)
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notNull := left.NotNull && right.NotNull
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// Apply database-specific type rules
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switch c.conf.Engine {
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case config.EngineMySQL:
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return combineMySQLTypes(left, right, operator, notNull)
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default:
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// TODO: Implement type inference for PostgreSQL and SQLite
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// For now, use conservative fallback rules
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return combineGenericTypes(left, right, operator, notNull)
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}
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}
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// combineMySQLTypes implements MySQL-specific type inference rules.
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//
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// Division always returns decimal or float:
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//
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// SELECT int_col / 1024 -- returns decimal
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// SELECT float_col / 1024 -- returns float
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// SELECT int_col DIV 1024 -- returns decimal (DIV is MySQL-specific)
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//
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// Nullability propagates (NULL op anything = NULL):
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//
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// nullable_col / 1024 -- returns nullable result
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// NOT NULL col / 1024 -- returns NOT NULL result
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func combineMySQLTypes(left, right *Column, operator string, notNull bool) *Column {
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// Handle nil operands
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if left == nil && right == nil {
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return nil
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}
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if left == nil {
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return right
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}
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if right == nil {
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return left
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}
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// Normalize MySQL-specific operators
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switch operator {
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case "div":
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operator = "/" // DIV is MySQL's integer division, but for type inference treat as division
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case "mod":
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operator = "%" // MOD is alias for %
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}
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switch operator {
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case "/":
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// Division: int/int = decimal, float/anything = float
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if isFloatType(left.DataType) || isFloatType(right.DataType) {
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return &Column{DataType: "float", NotNull: notNull}
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}
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return &Column{DataType: "decimal", NotNull: notNull}
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case "%":
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// Modulo: returns integer if both are integers, otherwise decimal
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if isIntegerType(left.DataType) && isIntegerType(right.DataType) {
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return &Column{DataType: "int", NotNull: notNull}
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}
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return &Column{DataType: "decimal", NotNull: notNull}
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case "&", "|", "<<", ">>", "~", "#", "^":
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// Bitwise operators: always integer
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return &Column{DataType: "int", NotNull: notNull}
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default:
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// Arithmetic: standard type promotion
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return promoteArithmeticTypes(left, right, notNull)
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}
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}
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// combineGenericTypes provides conservative fallback for unsupported databases.
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// Returns nil to avoid incorrect type assumptions for PostgreSQL, SQLite, etc.
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// This ensures fallback to the original behavior (interface{} or default types).
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func combineGenericTypes(left, right *Column, operator string, notNull bool) *Column {
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// TODO: Implement type inference for PostgreSQL and SQLite
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// For now, return nil to use safe defaults
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return nil
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}
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// promoteArithmeticTypes applies standard type promotion rules for arithmetic.
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// This follows the principle: int -> decimal -> float
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func promoteArithmeticTypes(left, right *Column, notNull bool) *Column {
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dataType := "int"
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// Float takes precedence over all other numeric types
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if isFloatType(left.DataType) || isFloatType(right.DataType) {
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dataType = "float"
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} else if isDecimalType(left.DataType) || isDecimalType(right.DataType) {
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// Decimal takes precedence over integer
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dataType = "decimal"
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} else if isIntegerType(left.DataType) && isIntegerType(right.DataType) {
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// Both are integers
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dataType = "int"
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}
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return &Column{
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DataType: dataType,
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NotNull: notNull,
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}
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}
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// isFloatType checks if a datatype is a floating-point type
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func isFloatType(dataType string) bool {
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switch dataType {
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case "float", "double", "double precision", "real":
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return true
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}
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return false
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}
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// isDecimalType checks if a datatype is a decimal/numeric type
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func isDecimalType(dataType string) bool {
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switch dataType {
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case "decimal", "numeric", "dec", "fixed":
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return true
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}
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return false
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}
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// isIntegerType checks if a datatype is an integer type
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func isIntegerType(dataType string) bool {
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switch dataType {
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case "int", "integer", "smallint", "bigint", "tinyint", "mediumint":
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return true
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}
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return false
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}

‎internal/compiler/output_columns.go‎

Lines changed: 22 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -150,12 +150,20 @@ func (c *Compiler) outputColumns(qc *QueryCatalog, node ast.Node) ([]*Column, er
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if res.Name != nil {
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name = *res.Name
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}
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switch op := astutils.Join(n.Name, ""); {
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op := astutils.Join(n.Name, "")
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switch {
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case lang.IsComparisonOperator(op):
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// TODO: Generate a name for these operations
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cols = append(cols, &Column{Name: name, DataType: "bool", NotNull: true})
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case lang.IsMathematicalOperator(op):
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cols = append(cols, &Column{Name: name, DataType: "int", NotNull: true})
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// Try to infer the type from operands
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if inferredCol := c.inferExprType(n, tables); inferredCol != nil {
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inferredCol.Name = name
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cols = append(cols, inferredCol)
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} else {
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// Fallback to previous behavior if inference fails
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cols = append(cols, &Column{Name: name, DataType: "int", NotNull: true})
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}
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default:
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cols = append(cols, &Column{Name: name, DataType: "any", NotNull: false})
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}
@@ -233,6 +241,17 @@ func (c *Compiler) outputColumns(qc *QueryCatalog, node ast.Node) ([]*Column, er
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shouldNotBeNull = true
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continue
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}
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// Try to infer the type of the argument
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if inferredCol := c.inferExprType(arg, tables); inferredCol != nil {
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if firstColumn == nil {
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firstColumn = inferredCol
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}
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shouldNotBeNull = shouldNotBeNull || inferredCol.NotNull
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continue
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}
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// Fallback to the old logic for simple column references
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if ref, ok := arg.(*ast.ColumnRef); ok {
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columns, err := outputColumnRefs(res, tables, ref)
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if err != nil {
@@ -247,6 +266,7 @@ func (c *Compiler) outputColumns(qc *QueryCatalog, node ast.Node) ([]*Column, er
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}
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}
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if firstColumn != nil {
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firstColumn.Name = name
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firstColumn.NotNull = shouldNotBeNull
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firstColumn.skipTableRequiredCheck = true
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cols = append(cols, firstColumn)

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