Relational databases store information in tables — with columns that are analogous to elements in a data structure and rows that are one instance of that data structure. In SQL, a table cell without a value contains a special marker, NULL, which is not the same as zero, an empty string, or any other kind of value that works with equality tests; i.e. NULL != 0
, NULL != "
“, etc. The SQL Coalesce statement is one way of processing these NULL values for common uses like text processing.
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