Mysql uses DATE_FORMAT to recover erroneous data.

Mysql uses DATE_FORMAT to recover erroneous data.

Because of the new development project, when colleagues create data, the time format is "20150708", but the expected data format is ".
The database uses mysql, and the time field type is varchar (10). Since there are hundreds of test data entries, it is unrealistic to modify them one by one. Three methods are provided for implementation, date_format is used for simple implementation.
The SQL statement is as follows:

UPDATE organ_book_resource obr SET obr. day = DATE_FORMAT (obr. day, '% Y-% m-% D ')

The other two solutions are too troublesome and have not been tried. The idea is as follows:
First, extract the string and then splice it with concat.
Second: Use the convert function.

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