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45 lines
1.4 KiB
Markdown
45 lines
1.4 KiB
Markdown
# 条件函数 {#tiao-jian-han-shu}
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## if(cond, then, else), cond ? operator then : else {#ifcond-then-else-cond-operator-then-else}
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如果`cond ！= 0`则返回`then`，如果`cond = 0`则返回`else`。
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`cond`必须是`UInt8`类型，`then`和`else`必须存在最低的共同类型。
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`then`和`else`可以是`NULL`
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## multiIf {#multiif}
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允许您在查询中更紧凑地编写[CASE](../operators.md#operator_case)运算符。
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multiIf(cond_1, then_1, cond_2, then_2...else)
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**参数:**
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- `cond_N` — 函数返回`then_N`的条件。
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- `then_N` — 执行时函数的结果。
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- `else` — 如果没有满足任何条件，则为函数的结果。
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该函数接受`2N + 1`参数。
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**返回值**
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该函数返回值«then\_N»或«else»之一，具体取决于条件`cond_N`。
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**示例**
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存在如下一张表
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┌─x─┬────y─┐
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│ 1 │ ᴺᵁᴸᴸ │
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│ 2 │ 3 │
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└───┴──────┘
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执行查询 `SELECT multiIf(isNull(y) x, y < 3, y, NULL) FROM t_null`。结果：
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┌─multiIf(isNull(y), x, less(y, 3), y, NULL)─┐
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│ 1 │
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│ ᴺᵁᴸᴸ │
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└────────────────────────────────────────────┘
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[来源文章](https://clickhouse.tech/docs/en/query_language/functions/conditional_functions/) <!--hide-->
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