Question

I have two tables with identical schema. Let’s name them TestTable and TestTableTemp. I need to copy just two columns from TestTableTemp to TestTable without disrupting other data. The rows in TestTable are a subset of those in TestTableTemp. Let’s say the columns that I need to copy are named Column1 and Column2 and that they have identical primary keys reference by column primaryKey.

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In mysql I believe this could be done as such or something similar:

UPDATE TestTable, TestTableTemp
SET TestTable.Column1 = TestTableTemp.Column1, TestTable.Column2 = TestTableTemp.Column2
WHERE TestTable.primaryKey = TestTableTemp.primaryKey

Sqlite does not allow for multiple tables to be defined on the update statement as can been seen in their reference data here: http://www.sqlite.org/lang_update.html

The best I could come up with is such:

UPDATE TestTable SET
Column1 = (select TestTableTemp.Column1 from TestTableTemp, TestTable where TestTable.primaryKey = TestTableTemp.primaryKey),
Column2 = (select TestTableTemp.Column2 from TestTableTemp, TestTable where TestTable.primaryKey = TestTableTemp.primaryKey) 
WHERE EXISTS(select * from TestTableTemp where TestTable.primaryKey = TestTableTemp.primaryKey"

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This gives me a syntax error near “.” I am guessing this is because I cannot reference TestTable in the scalar expressions.

Can anyone point me in the right direction? Any help is much appreciated.

EDIT:

I cleaned up the second query a bit. It seems to just set the Column1 and Column2 to the first row from that column from TestTableTemp.

Answer 1

Your original query for comparison:

UPDATE TestTable, TestTableTemp
   SET TestTable.Column1 = TestTableTemp.Column1
     , TestTable.Column2 = TestTableTemp.Column2
 WHERE TestTable.primaryKey = TestTableTemp.primaryKey

Here is the working query (I just slightly changed your version):

http://sqlfiddle.com/#!5/f3a19/9

UPDATE TestTable
SET

  Column1 = ( SELECT TestTableTemp.Column1
              FROM   TestTableTemp
              WHERE  TestTableTemp.primaryKey = TestTable.primaryKey )

 ,Column2 = ( SELECT TestTableTemp.Column2
              FROM   TestTableTemp
              WHERE  TestTableTemp.primaryKey = TestTable.primaryKey )

WHERE EXISTS( SELECT NULL
              FROM   TestTableTemp
              WHERE  TestTableTemp.primaryKey = TestTable.primaryKey )
;