Docs for concat

Author: jeffgbutler

CHANGELOG.md

@@ -51,8 +51,7 @@ The pull request for this change is ([#550](https://github.com/mybatis/mybatis-d
    algorithm. Also deprecated the constructors on SqlTable that accept Suppliers for table name - this creates an
    effectively mutable object and goes against the principles of immutability that we strive for in the library.
    ([#572](https://github.com/mybatis/mybatis-dynamic-sql/pull/572))
-      
-
+5. Add `SqlBuilder.concat` and the equivalent in Kotlin. This is a concatenate function that works on more databases. 
 
 ## Release 1.4.1 - October 7, 2022
 

src/main/java/org/mybatis/dynamic/sql/SqlBuilder.java

@@ -489,11 +489,30 @@ static <T> Subtract<T> subtract(BindableColumn<T> firstColumn, BasicColumn secon
         return Subtract.of(firstColumn, secondColumn, subsequentColumns);
     }
 
+    /**
+     * Concatenate function that renders as "(x || y || z)". This will not work on some
+     * databases like MySql. In that case, use {@link SqlBuilder#concat(BindableColumn, BasicColumn...)}
+     *
+     * @param firstColumn first column
+     * @param secondColumn second column
+     * @param subsequentColumns subsequent columns
+     * @return a Concatenate instance
+     * @param <T> type of column
+     */
     static <T> Concatenate<T> concatenate(BindableColumn<T> firstColumn, BasicColumn secondColumn,
             BasicColumn... subsequentColumns) {
         return Concatenate.concatenate(firstColumn, secondColumn, subsequentColumns);
     }
 
+    /**
+     * Concatenate function that renders as "concat(x, y, z)". This version works on more databases
+     * than {@link SqlBuilder#concatenate(BindableColumn, BasicColumn, BasicColumn...)}
+     *
+     * @param firstColumn first column
+     * @param subsequentColumns subsequent columns
+     * @return a Concat instance
+     * @param <T> type of column
+     */
     static <T> Concat<T> concat(BindableColumn<T> firstColumn, BasicColumn... subsequentColumns) {
         return Concat.concat(firstColumn, subsequentColumns);
     }

src/main/java/org/mybatis/dynamic/sql/select/function/OperatorFunction.java

@@ -50,7 +50,7 @@ protected OperatorFunction<T> copy() {
     public String renderWithTableAlias(TableAliasCalculator tableAliasCalculator) {
         String paddedOperator = " " + operator + " "; //$NON-NLS-1$ //$NON-NLS-2$
 
-        // note - the cast below is added for a type inference issues in some compilers
+        // note - the cast below is added for type inference issues in some compilers
         return Stream.of(Stream.of((BasicColumn) column), Stream.of(secondColumn), subsequentColumns.stream())
                 .flatMap(Function.identity())
                 .map(column -> column.renderWithTableAlias(tableAliasCalculator))