SELECT Table_1. , Table_2. , Table_3.* FROM ((Table_1 INNER JOIN Table_2 ON Table_1.DataTime = Table_2.DataTime) INNER JOIN Table_3 ON Table_2.DataTime = Table_3.DataTime) where Table_1.DataTime = 1
is not necessarily merging three tables with the same ID data
because I want to choose three tables with the same ID data to insert into another table, but sometimes some tables do not necessarily have the ID of the other two tables. All data inserts are wrong
always has the table with data as the main table. The other two are associated with left join. So it doesn't matter if the other two tables don't exist
INNER JOIN for fields associated with two tables, that is, foreign keys.
UNION ALL .
look at the structure of your tables in that way
or send out your watch knot and look at it for you
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