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Standard Library

XTDB provides a rich standard library of predicates and functions:

The following control structures are available in XTDB:

`CASE`

CASE takes two forms:

With a test-expr, CASE tests the result of the test-expr against each of the value-expr`s until a match is found - it then returns the value of the corresponding `result-expr.
```
CASE <test-expr>
  WHEN <value-expr> THEN <result-expr>
  [ WHEN ... ]
  [ ELSE <default-expr> ]
END
```
If no match is found, and a default-expr is present, it will return the value of that expression, otherwise it will return null.
With a series of predicates, CASE checks the value of each predicate expression in turn, until one is true - it then returns the value of the corresponding result-expr.
```
CASE
  WHEN <predicate> THEN <result-expr>
  [ WHEN ... ]
  [ ELSE <default-expr> ]
END
```
If none of the predicates return true, and a default-expr is present, it will return the value of that expression, otherwise it will return null.

`COALESCE` / `NULLIF`

COALESCE returns the first non-null value of its arguments:

COALESCE(<expr>, ...)

NULLIF returns null if expr1 equals expr2; otherwise it returns the value of expr1.

NULLIF(<expr1>, <expr2>)