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expression: fix unix_timestamp function which is not compatible with Mysql #9751

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expression: fix unix_timestamp function which is not compatible with Mysql #9751

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0cac052
Fix unixtimestamp function
wjhuang2016 Mar 15, 2019
3c24c9b
Add test
wjhuang2016 Mar 19, 2019
3768b5e
Style change
wjhuang2016 Mar 19, 2019
17c0043
Fix return type according to #9861
wjhuang2016 Mar 26, 2019
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8 changes: 4 additions & 4 deletions expression/builtin_time.go
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Original file line number Diff line number Diff line change
Expand Up @@ -3516,10 +3516,10 @@ func (c *unixTimestampFunctionClass) getFunction(ctx sessionctx.Context, args []
argType := args[0].GetType()
argEvaltp := argType.EvalType()
if argEvaltp == types.ETString {
// Treat types.ETString as unspecified decimal.
retDecimal = types.UnspecifiedLength
if cnst, ok := args[0].(*Constant); ok {
tmpStr, _, err := cnst.EvalString(ctx, chunk.Row{})
if _, ok := args[0].(*Column); ok {
retDecimal = types.UnspecifiedLength
} else {
tmpStr, _, err := args[0].EvalString(ctx, chunk.Row{})
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Consider this case: args[0] is a scalar function, but it refers to other columns. Directly calling args[0].EvalString() would cause a nil pointer deference panic because the input Row is empty in this case.

A simple SQL can be:

select unix_timestamp(concat(a+b)) from t;

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You're right, I think that some scalar functions would panic. And the test passing surprises we.
Can we eval it here for scalar function like concat?

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For general scalar function, I think we can not. We can specially handle the GetVar function in the non-prepare statements. However, it's better to check how mysql handle this scenario in their codebase.

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For general scalar function, I think we can not. We can specially handle the GetVar function in the non-prepare statements. However, it's better to check how mysql handle this scenario in their codebase.

Agree with you, we have better check the code in MySQL. And I think GetVar is not the only function we need to handle.

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@eurekaka eurekaka Apr 4, 2019 •
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An off-topic finding: concat seems to have bug currently

mysql> select concat(a+b) from t;
ERROR 1054 (42S22): Unknown column 'b' in 'field list'
mysql> select concat(a, b) from t;
ERROR 1054 (42S22): Unknown column 'b' in 'field list'
mysql> select unix_timestamp(concat(a+b)) from t;
ERROR 1054 (42S22): Unknown column 'b' in 'field list'

it reports error in parser.

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@eurekaka
Do you forget the column b when create table t?

mysql> create table t(a int, b int);
Query OK, 0 rows affected (0.04 sec)

mysql> select concat(a+b) from t;
Empty set (0.00 sec)

mysql> select concat(a, b) from t;
Empty set (0.01 sec)

mysql> select unix_timestamp(concat(a+b)) from t;
Empty set (0.01 sec)

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😭 My fault.

if err != nil {
return nil, err
}
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16 changes: 16 additions & 0 deletions expression/builtin_time_test.go
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Expand Up @@ -1616,6 +1616,22 @@ func (s *testEvaluatorSuite) TestUnixTimestamp(c *C) {
c.Assert(err, IsNil)
c.Assert(d.IsNull(), Equals, true)

// https://github.com/pingcap/tidb/issues/9729
// Test UNIX_TIMESTAMP(@a).
resetStmtContext(s.ctx)
s.ctx.GetSessionVars().Users["a"] = "1970-01-01 08:00:01"
args = []types.Datum{types.NewStringDatum("a")}
getVarFunc, err := newFunctionForTest(s.ctx, ast.GetVar, s.datumsToConstants(args)...)
c.Assert(err, IsNil)
funcArgs := make([]Expression, 0, 1)
funcArgs = append(funcArgs, getVarFunc)
f, err = fc.getFunction(s.ctx, funcArgs)
c.Assert(err, IsNil)
d, err = evalBuiltinFunc(f, chunk.Row{})
c.Assert(err, IsNil)
c.Assert(d.Kind(), Equals, types.KindInt64)
c.Assert(d.GetInt64(), Equals, int64(28801))

// Set the time_zone variable, because UnixTimestamp() result depends on it.
s.ctx.GetSessionVars().TimeZone = time.UTC
tests := []struct {
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