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21 sie 2010 · I'm having a problem where when I try to select the rows that have a NULL for a certain column, it returns an empty set. However, when I look at the table in phpMyAdmin, it says null for most of the rows. My query looks something like this: SELECT pid FROM planets WHERE userid = NULL Empty set every time.
6 cze 2024 · We can use the function NULLIF to compare and check if the column contains null or empty values: SELECT id, name FROM Department WHERE NULLIF(TRIM(code), '') IS NULL; The NULLIF function evaluates its two arguments, returning NULL if they are equal.
2 lut 2024 · To ascertain if a column is empty or null in SQL, use COALESCE (column, ”) or column IS NULL OR column = ”. These queries fetch rows where the specified column contains an empty string or null value, ensuring comprehensive coverage of both scenarios.
Functions for Use in SELECT and WHERE Clauses. A select_expression or where_definition in a SQL statement can consist of any expression using the functions described next. An expression that contains NULL always produces a NULL value unless otherwise indicated in the documentation for the operators and functions involved in the expression.
I tried the following: SELECT column_name. FROM information_schema.columns. WHERE table_name = "table_name". AND EXISTS (. SELECT DISTINCT column_name FROM table_name WHERE column_name IS NOT NULL. ) But this also returns the column names where all the entries are NULL.
Summary: in this tutorial, you will learn how to use the MySQL WHERE clause in the SELECT statement to filter rows from the result set. Introduction to MySQL WHERE clause The WHERE clause allows you to specify a search condition for the rows returned by a query.
An expression that contains NULL always produces a NULL value unless otherwise indicated in the documentation for the operators and functions involved in the expression. All columns in the following example return NULL: mysql> SELECT NULL, 1+NULL, CONCAT('Invisible',NULL);
