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Use type conversion functions in queries

This topic provides examples of how to use type conversion functions in queries.

Type conversion functions​

Type conversion functions convert one data type to another, such as between numeric types and string types, or between time types and string types.

Examples​

Convert a time string to a time type​

In seekdb, a time string can be directly assigned to a DATE type, and seekdb will automatically convert it to a time type. You can also use the CONVERT() or CAST() function to convert data types. Here is an example SQL statement:

SELECT CONVERT('2020-02-02 14:30:45', DATE)    t1
    , CONVERT('2020-02-02 14:30:45', TIME)      t2
    , CONVERT('2020-02-02 14:30:45', DATETIME)  t3
    , CAST('2020-02-02 14:30:45' AS DATE)       t4
    , CAST('2020-02-02 14:30:45' AS TIME)       t5
    , CAST('2020-02-02 14:30:45' AS DATETIME)   t6
\G

*************************** 1. row ***************************
t1: 2020-02-02
t2: 14:30:45
t3: 2020-02-02 14:30:45
t4: 2020-02-02
t5: 14:30:45
t6: 2020-02-02 14:30:45
1 row in set
info

You can use the DATE_FORMAT function to convert a time type to a string type.

Convert between numeric and string types​

In seekdb, you can use the CONVERT() or CAST() function to convert between numeric and string types.

SELECT CONVERT('3.1415926', DECIMAL)  n1
    , CAST('3.1415926' AS DECIMAL)      n2
    , CONVERT(3.1415926, CHAR(10))      s1
    , CAST(3.1414926 AS CHAR(10))       s2;
+----+----+-----------+-----------+
| n1 | n2 | s1        | s2        |
+----+----+-----------+-----------+
|  3 |  3 | 3.1415926 | 3.1414926 |
+----+----+-----------+-----------+
1 row in set

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