Add support for EXTRACT time/date function.

internal/jet/expression.go

@@ -263,6 +263,25 @@ func (p *betweenOperatorExpression) serialize(statement StatementType, out *SQLB
 	p.max.serialize(statement, out, FallTrough(options)...)
 }
 
+type customExpression struct {
+	ExpressionInterfaceImpl
+	parts []Serializer
+}
+
+func newCustomExpression(parts ...Serializer) Expression {
+	ret := customExpression{
+		parts: parts,
+	}
+	ret.ExpressionInterfaceImpl.Parent = &ret
+	return &ret
+}
+
+func (c *customExpression) serialize(statement StatementType, out *SQLBuilder, options ...SerializeOption) {
+	for _, expression := range c.parts {
+		expression.serialize(statement, out, options...)
+	}
+}
+
 type complexExpression struct {
 	ExpressionInterfaceImpl
 	expressions Expression

internal/jet/func_expression.go

@@ -492,6 +492,11 @@ func TO_TIMESTAMP(timestampzStr, format StringExpression) TimestampzExpression {
 
 //----------------- Date/Time Functions and Operators ---------------//
 
+// EXTRACT extracts time component from time expression
+func EXTRACT(field string, from Expression) Expression {
+	return newCustomExpression(Token("EXTRACT("), Token(field), Token("FROM"), from, Token(")"))
+}
+
 // CURRENT_DATE returns current date
 func CURRENT_DATE() DateExpression {
 	dateFunc := NewDateFunc("CURRENT_DATE")

internal/jet/serializer.go

@@ -96,3 +96,10 @@ func (s serializerImpl) serialize(statement StatementType, out *SQLBuilder, opti
 		clause.Serialize(statement, out, FallTrough(options)...)
 	}
 }
+
+// Token can be used to construct complex custom expressions
+type Token string
+
+func (t Token) serialize(statement StatementType, out *SQLBuilder, options ...SerializeOption) {
+	out.WriteString(string(t))
+}