Android之SQLite——update基于A表更新B表中的值
转载:http://stackoverflow.com/questions/3845718/sql-how-to-update-table-values-from-another-table-with-the-same-user-name
文章内容如下所示:
sql: how to update table values from another table with the same user name?
question:
I have two tables, with a same column named user_name, saying table_a, table_b. I want to, copy from table_b, column_b_1, column_b2, to table_b1, column_a_1, column_a_2, respectively, where the user_name is the same, how to do it in sql statement?
answer:
As long as you have suitable indexes in place this should work alright:
UPDATE table_aSET table_a.column_a_1 = (SELECT table_b.column_b_1 FROM table_b WHERE table_b.user_name = table_a.user_name ) , table_a.column_a_2 = (SELECT table_b.column_b_2 FROM table_b WHERE table_b.user_name = table_a.user_name )WHERE EXISTS ( SELECT * FROM table_b WHERE table_b.user_name = table_a.user_name )
UPDATE insqlite3does not support a FROM clause, which makes this a little more work than in other RDBMS.
If performance is not satisfactory, another option might be to build up new rows for table_a using a select and join with table_a into a temporary table. Then delete the data from table_a and repopulate from the temporary.
结果:经测试该方法可行。靠谱!赞一个!哈哈!
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