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Databases & SQL vocabulary · Tables, Schemas and Database Objects

NULL

Meaning in databases & SQL, with examples

/nʌl/nounCore term

In databases & SQL, NULL means: A special marker meaning that a value is missing or unknown. It is not the same as zero or an empty string.

In Turkish: NULL, boş değer, tanımsız değer

How it is used

Columns are 'nullable' or 'NOT NULL'. Because NULL means unknown, 'x = NULL' is never true; you must write 'IS NULL' or 'IS NOT NULL'. NULLs also affect results: COUNT(column) and AVG skip them, and functions like COALESCE replace them with a default.

Example sentences

  1. The query returned nothing because it used = NULL instead of IS NULL.

  2. Half of the customers have NULL in the phone column.

Common collocations

  • IS NULL
  • NOT NULL
  • nullable column
  • NULL value
  • allow NULLs
  • columnA vertical part of a table with a name and a data type, holding one kind of information for every row, such as email or created_at.
  • data typeThe kind of value a column can hold, such as whole numbers, text, dates or true/false values. It controls what can be stored and how much space it takes.
  • constraintA rule set on a table or column that the database enforces automatically, rejecting any data that would break it.
  • default valueThe value a column gets automatically when a new row is inserted without a value for that column, such as 0, 'pending' or the current time.

This word in other fields

The same English word can have a different meaning in another field:

More terms: Tables, Schemas and Database Objects

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