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Advanced learning of MySQL -- basics -- multi table query -- joint query
2022-07-07 00:34:00 【Magic pig 9898】
The joint query
This is very simple
select Field list from surface A …
union [all]
select Field list from surface B …
To put it bluntly , Is to merge the results of multiple queries , Form a new result set .
Precautions for joint query
- For joint queries , The number of columns in multiple tables must be consistent , The types of fields should also be consistent .
- union all All the data will be combined directly , and union The merged data will be de duplicated ( surface A And table B It's the same watch , Different conditions , and or It's the same )
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