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pingcap · Jul 27, 2021 · 5a4bf46 · 5a4bf46
1 parent 5c5b987
commit 5a4bf46
Showing 1 changed file with 2 additions and 0 deletions.
diff --git a/expression/builtin_control.go b/expression/builtin_control.go
@@ -197,6 +197,8 @@ func (c *caseWhenFunctionClass) getFunction(ctx sessionctx.Context, args []Expre
 	if fieldTp.EvalType().IsStringKind() && !isBinaryStr {
 		fieldTp.Charset, fieldTp.Collate = DeriveCollationFromExprs(ctx, args...)
 		if fieldTp.Charset == charset.CharsetBin && fieldTp.Collate == charset.CollationBin {
+			// When args are Json and Numerical type(eg. Int), the fieldTp is String.
+			// Both their charset/collation is binary, but the String need a default charset/collation.
 			fieldTp.Charset, fieldTp.Collate = charset.GetDefaultCharsetAndCollate()
 		}
 	} else {