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SQL?? NULL ?? ???? ????? ?? ?? ?? ??? ??? isnull ?? isnull ?? isnotnull? ???????. = ??! =; 1. ISNULL ?? ISNOTNULL? ???? SelectFromeeeswherePhoneisNull? ?? NULL ?? ??????. 2. Coalesce ?? Isnull? ???? NULL? ???? Coalesce (???, 'N/A')? ?? ? ?? NULL ?? ?????. 3. NULL? ?? ???? ???? COUNT ()? ?? ?? ????? Count (?)? ? ?? ?? ? ? ?????. 4. ?? ???
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MongoDB? ?? ??? ??? ??
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MySQL?? ???? ??????? ???? ??
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SQL?? ???? ? ? ???? ???? ??? ??? ??????
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SQL?? ??? ????? ??
SQLServer?? ??? ?? ??? ??? ??? Throw ?? ???? ????. 1. ?? ???? ??? (?? ????)? ???? ?? ??? ?? ??? ?? ??, ???, ???, ?? ? ?? ??? ??????. 2. ?????, ?? ??????? _message () ??? ?? ?? ???? ?????. 3. ??? ?? ??? ???? ??? ?? ?? ??? 50000. 5. ?? ?????? ??? ? ????
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MySQL? innodb_file_per_table ??? ??????
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? MySQL ??????? ???? ????? ??? ??????
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Redis ?????? ?? ?? ????? ??? ??? ? ?????
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phpmyadmin?? ?? ??? ???? ??
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SQL?? ????? ?? ?? ???? ??
?? ?? ???? ??? ?????? ???? ?? ????. CTE ? ROW_NUMBER ()? ???? ? ???? ? ?? ?? ???? ?????, ?? SQLServer, PostgreSQL ? MySQL8.0? ?????. CTE? ???? ??? ?? ???? ??? ?? ???? ???? ?? ???? ?? ? ? ????. MySQL ?? Sqlite??? ?? ??? ?? ?? ???? ???? ?? ?? ?? ?? ?? ??? ? ????. ?? ?? ??? ?? ?? ? ??? ?? ? ?? ?? ?? ??? ???????. ?? ??? ???? ?? ???? ???? SELECT? ???? ??? ?????? ????? ?? ?????? ? ??? ??? ??? ???? ???? ?? ??? ???????.
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MySQL??? ?? ??????? ?? ?? ?? ??
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MySQL? ?? ?? ???? ?? ?? ??? ??????
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