feat(spanner/spansql): add support for IFNULL expressions (#6389)

Co-authored-by: rahul2393 <rahulyadavsep92@gmail.com>

spanner/spansql/parser.go

@@ -3041,6 +3041,9 @@ func (p *parser) parseLit() (Expr, *parseError) {
 	case tok.caseEqual("IF"):
 		p.back()
 		return p.parseIfExpr()
+	case tok.caseEqual("IFNULL"):
+		p.back()
+		return p.parseIfNullExpr()
 	}
 
 	// Handle typed literals.
@@ -3183,6 +3186,30 @@ func (p *parser) parseIfExpr() (If, *parseError) {
 	return If{Expr: expr, TrueResult: trueResult, ElseResult: elseResult}, nil
 }
 
+func (p *parser) parseIfNullExpr() (IfNull, *parseError) {
+	if err := p.expect("IFNULL", "("); err != nil {
+		return IfNull{}, err
+	}
+
+	expr, err := p.parseExpr()
+	if err != nil {
+		return IfNull{}, err
+	}
+	if err := p.expect(","); err != nil {
+		return IfNull{}, err
+	}
+
+	nullResult, err := p.parseExpr()
+	if err != nil {
+		return IfNull{}, err
+	}
+	if err := p.expect(")"); err != nil {
+		return IfNull{}, err
+	}
+
+	return IfNull{Expr: expr, NullResult: nullResult}, nil
+}
+
 func (p *parser) parseArrayLit() (Array, *parseError) {
 	// ARRAY keyword is optional.
 	// TODO: If it is present, consume any <T> after it.

spanner/spansql/parser_test.go

@@ -440,6 +440,12 @@ func TestParseExpr(t *testing.T) {
 				ElseResult: False,
 			},
 		},
+		{`IFNULL(NULL, TRUE)`,
+			IfNull{
+				Expr:       Null,
+				NullResult: True,
+			},
+		},
 
 		// String literal:
 		// Accept double quote and single quote.

spanner/spansql/sql.go

@@ -744,6 +744,15 @@ func (i If) addSQL(sb *strings.Builder) {
 	sb.WriteString(")")
 }
 
+func (in IfNull) SQL() string { return buildSQL(in) }
+func (in IfNull) addSQL(sb *strings.Builder) {
+	sb.WriteString("IFNULL(")
+	in.Expr.addSQL(sb)
+	sb.WriteString(", ")
+	in.NullResult.addSQL(sb)
+	sb.WriteString(")")
+}
+
 func (b BoolLiteral) SQL() string { return buildSQL(b) }
 func (b BoolLiteral) addSQL(sb *strings.Builder) {
 	if b {

spanner/spansql/sql_test.go

@@ -671,6 +671,20 @@ func TestSQL(t *testing.T) {
 			`SELECT IF(1 < 2, TRUE, FALSE)`,
 			reparseQuery,
 		},
+		{
+			Query{
+				Select: Select{
+					List: []Expr{
+						IfNull{
+							Expr:       IntegerLiteral(10),
+							NullResult: IntegerLiteral(0),
+						},
+					},
+				},
+			},
+			`SELECT IFNULL(10, 0)`,
+			reparseQuery,
+		},
 	}
 	for _, test := range tests {
 		sql := test.data.SQL()

spanner/spansql/types.go

@@ -752,6 +752,14 @@ type If struct {
 func (If) isBoolExpr() {} // possibly bool
 func (If) isExpr()     {}
 
+type IfNull struct {
+	Expr       Expr
+	NullResult Expr
+}
+
+func (IfNull) isBoolExpr() {} // possibly bool
+func (IfNull) isExpr()     {}
+
 type BoolLiteral bool
 
 const (