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首頁 時間序列數據庫 TSDB 時序數據庫 InfluxDB? 版 InfluxQL介紹 數據探索 子查詢

子查詢

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子查詢是嵌套在另一個查詢的FROM子句中的查詢。使用子查詢將查詢作為條件應用在另一個查詢中。子查詢提供類似嵌套函數和SQL HAVING子句的功能。

語法

  1. SELECT_clause FROM ( SELECT_statement ) [...]

語法描述

TSDB For InfluxDB?首先執行子查詢，然后執行主查詢。

主查詢包含著子查詢，至少需要SELECT子句和FROM子句。主查詢支持本文檔中列出的所有子句。

子查詢在主查詢的FROM子句中，需要用括號將子查詢括起來。子查詢支持本文檔中列出的所有子句。

InfluxQL支持在主查詢中有多個嵌套的子查詢，示例語法如下：

  1. SELECT_clause FROM ( SELECT_clause FROM ( SELECT_statement ) [...] ) [...]

示例

計算多個MAX()值的SUM()

  1. > SELECT SUM("max") FROM (SELECT MAX("water_level") FROM "h2o_feet" GROUP BY "location")
  3. name: h2o_feet
  4. time                   sum
  5. ----                   ---
  6. 1970-01-01T00:00:00Z   17.169

該查詢返回每個location中water_level的最大值的總和。

TSDB For InfluxDB?首先執行子查詢，計算每個location的water_level的最大值：

  1. > SELECT MAX("water_level") FROM "h2o_feet" GROUP BY "location"
  2. name: h2o_feet
  4. tags: location=coyote_creek
  5. time                   max
  6. ----                   ---
  7. 2015-08-29T07:24:00Z   9.964
  9. name: h2o_feet
  10. tags: location=santa_monica
  11. time                   max
  12. ----                   ---
  13. 2015-08-29T03:54:00Z   7.205

然后，TSDB For InfluxDB?執行主查詢，計算這些最大值的總和：9.964 + 7.205 = 17.169。請注意，該主查詢指定max（而不是water_level）作為SUM()函數中的field key。

計算兩個field的差值的MEAN()

  1. > SELECT MEAN("difference") FROM (SELECT "cats" - "dogs" AS "difference" FROM "pet_daycare")
  3. name: pet_daycare
  4. time                   mean
  5. ----                   ----
  6. 1970-01-01T00:00:00Z   1.75

該查詢返回measurement pet_daycare中cats數量和dogs數量的差異的平均值。

TSDB For InfluxDB?首先執行子查詢，計算field cats中的值和field dogs中的值的差異，并將輸出列命名為difference：

  1. > SELECT "cats" - "dogs" AS "difference" FROM "pet_daycare"
  3. name: pet_daycare
  4. time                   difference
  5. ----                   ----------
  6. 2017-01-20T00:55:56Z   -1
  7. 2017-01-21T00:55:56Z   -49
  8. 2017-01-22T00:55:56Z   66
  9. 2017-01-23T00:55:56Z   -9

然后，TSDB For InfluxDB?執行主查詢，計算這些差值的平均值。請注意，該主查詢指定difference作為MEAN()函數中的field key。

計算多個MEAN()值并在這些值上加上條件

  1. > SELECT "all_the_means" FROM (SELECT MEAN("water_level") AS "all_the_means" FROM "h2o_feet" WHERE time >= '2015-08-18T00:00:00Z' AND time <= '2015-08-18T00:30:00Z' GROUP BY time(12m) ) WHERE "all_the_means" > 5
  3. name: h2o_feet
  4. time                   all_the_means
  5. ----                   -------------
  6. 2015-08-18T00:00:00Z   5.07625

該查詢返回water_level的所有大于5的平均值。

TSDB For InfluxDB?首先執行子查詢，計算從2015-08-18T00:00:00Z到2015-08-18T00:30:00Z water_level的平均值，并將結果按12分鐘的時間間隔進行分組，同時將輸出列命名為all_the_means：

  1. > SELECT MEAN("water_level") AS "all_the_means" FROM "h2o_feet" WHERE time >= '2015-08-18T00:00:00Z' AND time <= '2015-08-18T00:30:00Z' GROUP BY time(12m)
  3. name: h2o_feet
  4. time                   all_the_means
  5. ----                   -------------
  6. 2015-08-18T00:00:00Z   5.07625
  7. 2015-08-18T00:12:00Z   4.950749999999999
  8. 2015-08-18T00:24:00Z   4.80675

然后，TSDB For InfluxDB?執行主查詢，只返回那些大于5的平均值。請注意，該主查詢指定all_the_means作為SELECT子句中的field key。

計算多個DERIVATIVE()值的SUM()

  1. > SELECT SUM("water_level_derivative") AS "sum_derivative" FROM (SELECT DERIVATIVE(MEAN("water_level")) AS "water_level_derivative" FROM "h2o_feet" WHERE time >= '2015-08-18T00:00:00Z' AND time <= '2015-08-18T00:30:00Z' GROUP BY time(12m),"location") GROUP BY "location"
  3. name: h2o_feet
  4. tags: location=coyote_creek
  5. time                   sum_derivative
  6. ----                   --------------
  7. 1970-01-01T00:00:00Z   -0.4950000000000001
  9. name: h2o_feet
  10. tags: location=santa_monica
  11. time                   sum_derivative
  12. ----                   --------------
  13. 1970-01-01T00:00:00Z   -0.043999999999999595

該查詢返回每個location中water_level的平均值的導數之和。

TSDB For InfluxDB?首先執行子查詢，計算以12分鐘為間隔獲取的water_level的平均值的導數，它對每個location都進行了計算，并將輸出列命名為water_level_derivative：

  1. > SELECT DERIVATIVE(MEAN("water_level")) AS "water_level_derivative" FROM "h2o_feet" WHERE time >= '2015-08-18T00:00:00Z' AND time <= '2015-08-18T00:30:00Z' GROUP BY time(12m),"location"
  3. name: h2o_feet
  4. tags: location=coyote_creek
  5. time                   water_level_derivative
  6. ----                   ----------------------
  7. 2015-08-18T00:12:00Z   -0.23800000000000043
  8. 2015-08-18T00:24:00Z   -0.2569999999999997
  10. name: h2o_feet
  11. tags: location=santa_monica
  12. time                   water_level_derivative
  13. ----                   ----------------------
  14. 2015-08-18T00:12:00Z   -0.0129999999999999
  15. 2015-08-18T00:24:00Z   -0.030999999999999694

然后，TSDB For InfluxDB?執行主查詢，計算每個location的water_level_derivative的總和。請注意，該主查詢指定water_level_derivative（而不是water_level或derivative）作為SUM()函數中的field key。

子查詢的常見問題

在子查詢中有多個SELECT語句

InfluxQL支持在主查詢中有多個嵌套的子查詢：

  1. SELECT_clause FROM ( SELECT_clause FROM ( SELECT_statement ) [...] ) [...]
  2.                      ------------------   ----------------
  3.                          Subquery 1          Subquery 2

InfluxQL不支持在子查詢中有多個SELECT語句：

  1. SELECT_clause FROM (SELECT_statement; SELECT_statement) [...]

如果在子查詢中有多個SELECT語句，那么系統會返回解析錯誤。


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