Details
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Bug
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Status: Closed (View Workflow)
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Major
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Resolution: Duplicate
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5.5, 10.0, 10.1, 10.2
Description
DROP TABLE IF EXISTS t1;
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CREATE TABLE t1 (val bit(1));
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INSERT INTO t1 VALUES (0);
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DROP TABLE IF EXISTS t2;
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CREATE TABLE t2 AS SELECT COALESCE(val, 1) AS c FROM t1;
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SELECT * FROM t2;
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SHOW CREATE TABLE t2;
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returns
+------+
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| c |
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+------+
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| 0 |
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+------+
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+-------+--------------------------------------------------------------------------------------------+
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| Table | Create Table |
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+-------+--------------------------------------------------------------------------------------------+
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| t2 | CREATE TABLE `t2` (
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`c` decimal(1,0) DEFAULT NULL
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) ENGINE=InnoDB DEFAULT CHARSET=latin1 |
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+-------+--------------------------------------------------------------------------------------------+
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Now if I run "mysql --column-type-info test" and execute this query:
SELECT COALESCE(val, 1) FROM t1;
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it returns the following result and metadata:
+------------------+
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| COALESCE(val, 1) |
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+------------------+
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| 0 |
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+------------------+
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Field 1: `COALESCE(val, 1)`
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...
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Type: VAR_STRING
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Collation: binary (63)
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Length: 1
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Max_length: 1
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Decimals: 31
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Flags: UNSIGNED BINARY
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Notice, COALESCE(val,1) positions itself as:
- DECIMAL(1,0) in CREATE TABLE...SELECT
- VARBINARY(1) in metadata returned by SELECT
The expected result is to return the same data type in both cases
Note, a UNION between a BIT column and an INT literal creates a column of type VARBINARY(20):
DROP TABLE IF EXISTS t1, t2;
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CREATE TABLE t1 (val BIT(1));
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CREATE TABLE t2 AS SELECT val FROM t1 UNION SELECT 1;
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SHOW CREATE TABLE t2;
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+-------+-----------------------------------------------------------------------------------------------+
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| Table | Create Table |
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+-------+-----------------------------------------------------------------------------------------------+
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| t2 | CREATE TABLE `t2` (
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`val` varbinary(20) DEFAULT NULL
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) ENGINE=InnoDB DEFAULT CHARSET=latin1 |
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+-------+-----------------------------------------------------------------------------------------------+
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which is closer to what metadata returns for COALESCE(val,1) rather than what CREATE TABLE..SELECT returns for COALESCE(val,1).
Summary:
- SELECT bit_column FROM t1 - returns a string-alike value with BIT type in metadata
- SELECT bit_column FROM t1 UNION SELECT 1 – returns a number-alike value with VAR_STRING data type in metadata
- SELECT COALESCE(bit_column,1) FROM t1 – returns a number-alike value with VAR_STRING metadata
- CREATE TABLE t2 AS SELECT val FROM t1 UNION SELECT 1; – creates a column of type VARBINARY(20), with number-alike values
- CREATE TABLE t2 AS SELECT COALESCE(val,1) FROM t1; – creates a column of type DECIMAL(1,0)
Attachments
Issue Links
- duplicates
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- Closed
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- relates to
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- Closed
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