pgstmt: impl select exists (#41)

Author: acoshift

pgstmt/select.go

@@ -12,6 +12,7 @@ type SelectStatement interface {
 	Distinct() Distinct
 	Columns(col ...any)
 	ColumnSelect(f func(b SelectStatement), as string)
+	ColumnExists(f func(b SelectStatement))
 	From(table ...string)
 	FromSelect(f func(b SelectStatement), as string)
 	FromValues(f func(b Values), as string)
@@ -103,6 +104,15 @@ func (st *selectStmt) ColumnSelect(f func(b SelectStatement), as string) {
 	st.columns.push(&b)
 }
 
+func (st *selectStmt) ColumnExists(f func(b SelectStatement)) {
+	var x selectStmt
+	f(&x)
+
+	var b buffer
+	b.push("exists", paren(x.make()))
+	st.columns.push(&b)
+}
+
 func (st *selectStmt) From(table ...string) {
 	st.from.pushString(table...)
 }

pgstmt/select_test.go

@@ -546,6 +546,26 @@ func TestSelect(t *testing.T) {
 			`,
 			[]any{1},
 		},
+		{
+			"select exists",
+			pgstmt.Select(func(b pgstmt.SelectStatement) {
+				b.ColumnExists(func(b pgstmt.SelectStatement) {
+					b.Columns("1")
+					b.From("table1")
+					b.Where(func(b pgstmt.Cond) {
+						b.Eq("t1", 1)
+					})
+				})
+			}),
+			`
+				select exists (
+					select 1
+					from table1
+					where (t1 = $1)
+				)
+			`,
+			[]any{1},
+		},
 	}
 
 	for _, tC := range cases {