Performance differences between IN and EXISTS
I often hear people wondering whether the EXISTS or the IN operator is better. Let's start by saying that the two operators behave differently when NULL values are involved (see this post).…
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Oracle
Writing about Oracle.
NOT IN vs. NOT EXISTS when NULL values are involved
NOT IN does not behave as you would expect when NULL values are involved. Suppose you have the following tables: CDFIELD DSFIELD 1 ALPHA 2 BETA TABLEA CDFIELD DSFIELD 1 GAMMA NULL DELTA…
Read articleHow to compute a timestamp in Oracle (PL/SQL)
Many sources use the term timestamp to refer specifically to Unix time, the number of seconds since 00:00:00 UTC on January 1, 1970. In Oracle you can compute this number very easily. For…
Read articleHow to create a copy/backup of a table in Oracle
You can create a backup of a table (structure and data) in Oracle by using the following syntax: The previous example creates the customersbackup table which mirrors the structure and data…
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