cherry pick pingcap#31806 to release-5.3

Signed-off-by: ti-srebot <ti-srebot@pingcap.com>

cmd/explaintest/r/collation.result

@@ -13,3 +13,25 @@ coercibility(convert('a' using utf8mb4))
 select coercibility(convert('a' using utf8mb4) collate utf8mb4_general_ci);
 coercibility(convert('a' using utf8mb4) collate utf8mb4_general_ci)
 0
+DROP TABLE IF EXISTS t2;
+CREATE TABLE t2 (
+id INT NOT NULL PRIMARY KEY auto_increment,
+`col_91` char(47) CHARACTER SET utf8 COLLATE utf8_bin NOT NULL,
+`col_92` int(10) unsigned DEFAULT '2478966067',
+`col_97` char(32) COLLATE utf8mb4_bin NOT NULL
+) collate utf8mb4_general_ci;
+INSERT INTO `t2` VALUES (17,'UUtJeaV',497551109,'snRXXCZHBPW');
+SET names utf8mb4 collate utf8mb4_bin;
+SELECT greatest( col_91 , col_97 ) as expr1 FROM t2 ORDER BY id;
+expr1
+snRXXCZHBPW
+SELECT least( col_91 , col_97 ) as expr1 FROM t2 ORDER BY id;
+expr1
+UUtJeaV
+SET names utf8mb4 collate utf8mb4_general_ci;
+SELECT greatest( col_91 , col_97 ) as expr1 FROM t2 ORDER BY id;
+expr1
+snRXXCZHBPW
+SELECT least( col_91 , col_97 ) as expr1 FROM t2 ORDER BY id;
+expr1
+UUtJeaV

cmd/explaintest/t/collation.test

@@ -6,4 +6,22 @@ insert into t values ('啊', '撒旦');
 select coercibility(concat(a, b)) from t;
 select coercibility(convert(concat(a, b) using utf8mb4) collate utf8mb4_general_ci) from t;
 select coercibility(convert('a' using utf8mb4));
-select coercibility(convert('a' using utf8mb4) collate utf8mb4_general_ci);
+select coercibility(convert('a' using utf8mb4) collate utf8mb4_general_ci);
+
+# test greatest and least function with collation.
+DROP TABLE IF EXISTS t2;
+CREATE TABLE t2 (
+    id INT NOT NULL PRIMARY KEY auto_increment,
+  `col_91` char(47) CHARACTER SET utf8 COLLATE utf8_bin NOT NULL,
+  `col_92` int(10) unsigned DEFAULT '2478966067',
+  `col_97` char(32) COLLATE utf8mb4_bin NOT NULL
+) collate utf8mb4_general_ci;
+
+INSERT INTO `t2` VALUES (17,'UUtJeaV',497551109,'snRXXCZHBPW');
+
+SET names utf8mb4 collate utf8mb4_bin;
+SELECT greatest( col_91 , col_97 ) as expr1 FROM t2 ORDER BY id;
+SELECT least( col_91 , col_97 ) as expr1 FROM t2 ORDER BY id;
+SET names utf8mb4 collate utf8mb4_general_ci;
+SELECT greatest( col_91 , col_97 ) as expr1 FROM t2 ORDER BY id;
+SELECT least( col_91 , col_97 ) as expr1 FROM t2 ORDER BY id;

expression/collation.go

@@ -194,7 +194,7 @@ func deriveCoercibilityForColumn(c *Column) Coercibility {
 
 func deriveCollation(ctx sessionctx.Context, funcName string, args []Expression, retType types.EvalType, argTps ...types.EvalType) (ec *ExprCollation, err error) {
 	switch funcName {
-	case ast.Concat, ast.ConcatWS, ast.Lower, ast.Lcase, ast.Reverse, ast.Upper, ast.Ucase, ast.Quote, ast.Coalesce:
+	case ast.Concat, ast.ConcatWS, ast.Lower, ast.Lcase, ast.Reverse, ast.Upper, ast.Ucase, ast.Quote, ast.Coalesce, ast.Greatest, ast.Least:
 		return CheckAndDeriveCollationFromExprs(ctx, funcName, retType, args...)
 	case ast.Left, ast.Right, ast.Repeat, ast.Trim, ast.LTrim, ast.RTrim, ast.Substr, ast.SubstringIndex, ast.Replace, ast.Substring, ast.Mid, ast.Translate:
 		return CheckAndDeriveCollationFromExprs(ctx, funcName, retType, args[0])

expression/collation_test.go

@@ -565,7 +565,7 @@ func TestDeriveCollation(t *testing.T) {
 		},
 		{
 			[]string{
-				ast.Concat, ast.ConcatWS, ast.Coalesce, ast.In,
+				ast.Concat, ast.ConcatWS, ast.Coalesce, ast.In, ast.Greatest, ast.Least,
 			},
 			[]Expression{
 				newConstString("a", CoercibilityCoercible, charset.CharsetUTF8MB4, charset.CollationUTF8MB4),