feat: EXPOSED-681 Add support for GREATEST and LEAST functions

Adds support for GREATEST(X, Y) and LEAST(X, Y) functions.
In SQLite, these are named MAX(X, Y) and MIN(X, Y), respectively.
(because you just had to be different, huh sqlite?)

exposed-core/src/main/kotlin/org/jetbrains/exposed/sql/Op.kt

@@ -299,6 +299,30 @@ class IsDistinctFromOp(
     }
 }
 
+/**
+ * Represents an SQL operator that returns the greatest (maximum) of [expr1] and [expr2].
+ */
+class GreatestOp<T, S : T>(
+    val expr1: Expression<T>,
+    val expr2: Expression<S>,
+) : Op<T>() {
+    override fun toQueryBuilder(queryBuilder: QueryBuilder): Unit = queryBuilder {
+        currentDialect.functionProvider.greatest(expr1, expr2, queryBuilder)
+    }
+}
+
+/**
+ * Represents an SQL operator that returns the least (minimum) of [expr1] and [expr2].
+ */
+class LeastOp<T, S : T>(
+    val expr1: Expression<T>,
+    val expr2: Expression<S>,
+) : Op<T>() {
+    override fun toQueryBuilder(queryBuilder: QueryBuilder): Unit = queryBuilder {
+        currentDialect.functionProvider.least(expr1, expr2, queryBuilder)
+    }
+}
+
 // Mathematical Operators
 
 /**

exposed-core/src/main/kotlin/org/jetbrains/exposed/sql/SQLExpressionBuilder.kt

@@ -579,6 +579,26 @@ interface ISqlExpressionBuilder {
         other: ExpressionWithColumnType<E>
     ): IsDistinctFromOp = IsDistinctFromOp(this, other)
 
+    /**
+     * The greatest (maximum) of this expression and [t].
+     */
+    infix fun <T> ExpressionWithColumnType<T>.greatest(t: T): GreatestOp<T, T> = GreatestOp(this, wrap(t))
+
+    /**
+     * The greatest (maximum) of this expression and [other].
+     */
+    infix fun <T, S : T> ExpressionWithColumnType<T>.greatest(other: Expression<S>): GreatestOp<T, S> = GreatestOp(this, other)
+
+    /**
+     * The least (minimum) of this expression and [t].
+     */
+    infix fun <T> ExpressionWithColumnType<T>.least(t: T): LeastOp<T, T> = LeastOp(this, wrap(t))
+
+    /**
+     * The least (minimum) of this expression and [other].
+     */
+    infix fun <T, S : T> ExpressionWithColumnType<T>.least(other: Expression<S>): LeastOp<T, S> = LeastOp(this, other)
+
     // Mathematical Operators
 
     /** Adds the [t] value to this expression. */

exposed-core/src/main/kotlin/org/jetbrains/exposed/sql/vendors/FunctionProvider.kt

@@ -34,6 +34,28 @@ abstract class FunctionProvider {
      */
     open fun random(seed: Int?): String = "RANDOM(${seed?.toString().orEmpty()})"
 
+    /**
+     * SQL function that returns the greatest (maximum) of two values.
+     *
+     * @param expr1 The first value.
+     * @param expr2 The second value.
+     * @param queryBuilder Query builder to append the SQL function to.
+     */
+    open fun <T, S : T> greatest(expr1: Expression<T>, expr2: Expression<S>, queryBuilder: QueryBuilder): Unit = queryBuilder {
+        append("GREATEST(", expr1, ", ", expr2, ")")
+    }
+
+    /**
+     * SQL function that returns the least (minimum) of two values.
+     *
+     * @param expr1 The first value.
+     * @param expr2 The second value.
+     * @param queryBuilder Query builder to append the SQL function to.
+     */
+    open fun <T, S : T> least(expr1: Expression<T>, expr2: Expression<S>, queryBuilder: QueryBuilder): Unit = queryBuilder {
+        append("LEAST(", expr1, ", ", expr2, ")")
+    }
+
     // String functions
 
     /**

exposed-core/src/main/kotlin/org/jetbrains/exposed/sql/vendors/SQLiteDialect.kt

@@ -25,6 +25,14 @@ internal object SQLiteDataTypeProvider : DataTypeProvider() {
 
 @Suppress("TooManyFunctions")
 internal object SQLiteFunctionProvider : FunctionProvider() {
+    override fun <T, S : T> greatest(expr1: Expression<T>, expr2: Expression<S>, queryBuilder: QueryBuilder) = queryBuilder {
+        append("MAX(", expr1, ", ", expr2, ")")
+    }
+
+    override fun <T, S : T> least(expr1: Expression<T>, expr2: Expression<S>, queryBuilder: QueryBuilder) = queryBuilder {
+        append("MIN(", expr1, ", ", expr2, ")")
+    }
+
     override fun <T : String?> charLength(expr: Expression<T>, queryBuilder: QueryBuilder) = queryBuilder {
         append("LENGTH(", expr, ")")
     }