if-not-exists is a common SQL condition used to check if an entity exists.

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MySQL: NOT EXISTS vs LEFT OUTER JOIN…IS NULL

Is NOT EXISTS or LEFT OUTER JOIN...IS NULL more efficient for finding records in one table that aren't in another? Specifically, I'm trying to figure out which of the two queries below is better: ...
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select string that doesn't contain a substring/field

TableA.content is varchar2(4000), which was populated from a CLOB value that contains markup and text for a website, paragraphs actually. TableB.keyword contains a string that I want to find in ...
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Adding a constant IF not in an other table

So I have this query. SELECT * FROM `Comment` WHERE `Target` = '".$_GET['pp']."' AND `Id` NOT IN (SELECT `Target` FROM `Delete` WHERE `Type` = 'comment') ORDER ...
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select columns if a column has a value

I have RegiNum and EmpNum columns in users table. If RegiNum column has a value it's considered as a student. If RegiNum is filled, I want to select Name and ID from that table. I used select ...
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Combine WHERE NOT EXISTS with ON DUPLICATE KEY UPDATE

I have 2 tables uz_params and uz_params_exceptions where uz_params is supposed to be updated frequently by an external script. INSERT INTO uz_params (extension, type, subtype, paramvalue) VALUES ...
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Conditional select needed

I have something like: SELECT ((SELECT SUM(VAL_TOTALA_FEROASE+VAL_TOTALA_NEFEROASE+VAL_TOTALA_ALTELE1+VAL_TOTALA_ALTELE2+ ...