Conditional#
Function |
Description |
|---|---|
Returns the first non-null value in the provided values/columns. |
|
Returns the greatest value in the list of expressions. |
|
Returns expr1 if the boolean condition provided as the first parameter evaluates to true, and expr2 otherwise. |
|
If an expression value is NULL, return an alternative value. |
|
Returns the smallest value in the list of expressions. |
|
Returns NULL if two expressions are equal, otherwise returns the first. |
COALESCE#
Returns the first non-null value in the provided values/columns.
Example:
df = pl.DataFrame(
{
"foo": [1, None, 3, None],
"bar": [1, 2, None, 4],
}
)
df.sql("""
SELECT foo, bar, COALESCE(foo, bar) AS baz FROM self
""")
# shape: (4, 3)
# ┌──────┬──────┬─────┐
# │ foo ┆ bar ┆ baz │
# │ --- ┆ --- ┆ --- │
# │ i64 ┆ i64 ┆ i64 │
# ╞══════╪══════╪═════╡
# │ 1 ┆ 1 ┆ 1 │
# │ null ┆ 2 ┆ 2 │
# │ 3 ┆ null ┆ 3 │
# │ null ┆ 4 ┆ 4 │
# └──────┴──────┴─────┘
GREATEST#
Returns the greatest value in the list of expressions.
Example:
df = pl.DataFrame(
{
"foo": [100, 200, 300, 400],
"bar": [20, 10, 30, 40]
}
)
df.sql("""
SELECT GREATEST(foo, bar) AS baz FROM self
""")
# shape: (4, 1)
# ┌─────┐
# │ baz │
# │ --- │
# │ i64 │
# ╞═════╡
# │ 100 │
# │ 200 │
# │ 300 │
# │ 400 │
# └─────┘
IF#
Returns expr1 if the boolean condition provided as the first parameter evaluates to true, and expr2 otherwise.
Example:
df = pl.DataFrame(
{
"foo": [100, 200, 300, 400],
"bar": [10, 20, 30, 40]
}
)
df.sql("""
SELECT IF(foo < 250, 111, 999) AS baz FROM self
""")
# shape: (4, 1)
# ┌─────┐
# │ baz │
# │ --- │
# │ i32 │
# ╞═════╡
# │ 111 │
# │ 111 │
# │ 999 │
# │ 999 │
# └─────┘
IFNULL#
If an expression value is NULL, return an alternative value.
Example:
df = pl.DataFrame(
{
"foo": ["a", None, None, "d"],
"bar": [1, 2, 3, 4],
}
)
df.sql("""
SELECT IFNULL(foo, 'n/a') AS baz FROM self
""")
# shape: (4, 1)
# ┌─────┐
# │ baz │
# │ --- │
# │ str │
# ╞═════╡
# │ a │
# │ n/a │
# │ n/a │
# │ d │
# └─────┘
LEAST#
Returns the smallest value in the list of expressions.
Example:
df = pl.DataFrame(
{
"foo": [100, 200, 300, 400],
"bar": [20, 10, 30, 40]
}
)
df.sql("""
SELECT LEAST(foo, bar) AS baz FROM self
""")
# shape: (4, 1)
# ┌─────┐
# │ baz │
# │ --- │
# │ i64 │
# ╞═════╡
# │ 20 │
# │ 10 │
# │ 30 │
# │ 40 │
# └─────┘
NULLIF#
Returns NULL if two expressions are equal, otherwise returns the first.
Example:
df = pl.DataFrame(
{
"foo": [100, 200, 300, 400],
"bar": [20, 10, 30, 40]
}
)
df.sql("""
SELECT NULLIF(foo, bar) AS baz FROM self
""")
# shape: (4, 1)
# ┌─────┐
# │ baz │
# │ --- │
# │ i64 │
# ╞═════╡
# │ 100 │
# │ 200 │
# │ 300 │
# │ 400 │
# └─────┘