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ddl: prohibit modification decimal precision to avoid inconsistency problem #10433

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merged 4 commits into from
May 14, 2019
Merged

ddl: prohibit modification decimal precision to avoid inconsistency problem #10433

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ddl: prohibit modification decimal precision to avoid inconsistency p…
crazycs520 May 13, 2019
5cf6c6e
Address comment
crazycs520 May 13, 2019
964aa38
Merge branch 'master' into alter-decimal
crazycs520 May 13, 2019
5682274
Merge branch 'master' into alter-decimal
zimulala May 14, 2019
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2 changes: 2 additions & 0 deletions ddl/column_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -934,6 +934,8 @@ func (s *testColumnSuite) TestModifyColumn(c *C) {
{"varchar(10)", "varchar(8)", errUnsupportedModifyColumn.GenWithStackByArgs("length 8 is less than origin 10")},
{"varchar(10)", "varchar(11)", nil},
{"varchar(10) character set utf8 collate utf8_bin", "varchar(10) character set utf8", nil},
{"decimal(2,1)", "decimal(3,2)", errUnsupportedModifyColumn.GenWithStack("unsupported modify decimal column precision")},
{"decimal(2,1)", "decimal(2,1)", nil},
}
for _, tt := range tests {
ftA := s.colDefStrToFieldType(c, tt.origin)
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4 changes: 4 additions & 0 deletions ddl/ddl_api.go
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Expand Up @@ -2192,6 +2192,10 @@ func modifiableCharsetAndCollation(toCharset, toCollate, origCharset, origCollat
// It returns true if the two types has the same Charset and Collation, the same sign, both are
// integer types or string types, and new Flen and Decimal must be greater than or equal to origin.
func modifiable(origin *types.FieldType, to *types.FieldType) error {
// Because EncodeDecimal encodes the precision information, if change the decimal precision, need rewrite the record.
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The root cause is modifying decimal precision needs to rewrite binary representation of that decimal?

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done.

if origin.Tp == mysql.TypeNewDecimal && (to.Flen != origin.Flen || to.Decimal != origin.Decimal) {
return errUnsupportedModifyColumn.GenWithStack("unsupported modify decimal column precision")
}
if to.Flen > 0 && to.Flen < origin.Flen {
msg := fmt.Sprintf("length %d is less than origin %d", to.Flen, origin.Flen)
return errUnsupportedModifyColumn.GenWithStackByArgs(msg)
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10 changes: 10 additions & 0 deletions executor/admin_test.go
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Expand Up @@ -505,6 +505,16 @@ func (s *testSuite1) TestAdminCheckTable(c *C) {
tk.MustExec(`alter table t1 add column b timestamp not null;`)
tk.MustExec(`alter table t1 add index(b);`)
tk.MustExec(`admin check table t1;`)

// Test for index with change decimal precision.
tk.MustExec(`drop table if exists t1`)
tk.MustExec(`create table t1 (a decimal(2,1), index(a))`)
tk.MustExec(`insert into t1 set a='1.9'`)
_, err = tk.Exec(`alter table t1 modify column a decimal(3,2);`)
c.Assert(err, NotNil)
c.Assert(err.Error(), Equals, "[ddl:203]unsupported modify decimal column precision")
tk.MustExec(`delete from t1;`)
tk.MustExec(`admin check table t1;`)
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Why check table after all rows have been deleted?

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tidb> create table t1 (a decimal(2,1), index(a))
Query OK, 0 rows affected
Time: 0.070s
tidb> insert into t1 set a='-3.9'
Query OK, 1 row affected
Time: 0.009s
tidb> alter table t1 modify column a DECIMAL(22, 3);
Query OK, 0 rows affected
Time: 0.065s
tidb> delete from t1;
Query OK, 1 row affected
Time: 0.003s
tidb> admin check table t1
(8003, u't1 err:[admin:1]index:&admin.RecordData{Handle:1, Values:[]types.Datum{types.Datum{k:0x8, collation:0x0, decimal:0x1, length:0x2, i:0, b:[]uint8(nil), x:(*types.MyDecimal)(0xc000ab48a0)}}} != record:<nil>')

}

func (s *testSuite1) TestAdminCheckPrimaryIndex(c *C) {
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