PostgreSQL 的 count(distinct …) 的实现方式是排序而不是使用 hash, 所以速度很慢. 应该要换成 hash 方式, 只是因为各种原因还没有实现. 规避途径一: 通过 COUNT 子查询 使用下面的方式, 查询时间能缩短一半以上 SELECT COUNT(col) FROM ( SELECT DISTINCT field_1 AS col FROM table_1 ) TEMP 1. 2. ...
data_len; int hoff; bool hasnull = false; int numberOfAttributes = tupleDescriptor->natts; int i; if (numberOfAttributes > MaxTupleAttributeNumber) ereport(ERROR, (errcode(ERRCODE_TOO_MANY_COLUMNS), errmsg
DIAGNOSTICS r_count :=row_count;--获取操作行数ENDIF;-- DROP TABLE Project; --最后需要DROP临时表IF r_count>0THENRETURN1;ELSERETURN0;ENDIF;ELSERETURN-1;ENDIF;END; $function$ ; XML参数格式 <xml xmlns="xmlns"> <itemid="5f303b8c0001"/> <itemid="5f303b980002"/> </xml>...
For example, if you have multiple columns in several tables that should be an between 0 and 255, you could use a custom data type so that you only have to define the constraints once. Or, if you have complex data - like metadata about a file - and you want to save it to a ...
-- SetupCREATETABLEaggtest(aINT,btext);INSERTINTOaggtestSELECTa,md5((b%100)::text)FROMgenerate_series(1,10)a,generate_series(1,100000)b;CREATEINDEXONaggtest(a,b);VACUUM FREEZEANALYZEaggtest;EXPLAIN(ANALYZE,COSTSOFF,TIMINGOFF,BUFFERS)SELECTa,COUNT(DISTINCTb)FROMaggtestGROUPBYa...
The result of a SQL command yielding a single row (possibly of multiple columns) can be assigned to a record variable, row-type variable, or list of scalar variables. This is done by writing the base SQL command and adding an INTO clause. For example, SELECT select_expressions INTO [STR...
some_query: | query: | SELECT current_database() as datname, count(*) as rows FROM some_table metrics: - datname: usage: "LABEL" description: "Name of current database" - rows: usage: "GAUGE" description: "number of rows" target_databases: - "*" - "template1" The above example...
. We'll add this to the Q&A section of this issue.While you can now change data types of columns in tables - you are somewhat limited as to what you can change them to instead of the Microsoft SQL Server way of - yah you can change it to anything, but if cast of existing data ...
How to Index JSONB Columns in PostgreSQLHow to Monitor and Optimize PostgreSQL Index PerformancePostgreSQL Performance Tuning: Optimizing Database IndexesOptimizing Array Queries With GIN Indexes in PostgreSQLSQL/JSON Data Model and JSON in SQL: A PostgreSQL PerspectiveHow to Query JSON Metadata in Post...
Let’s see how the statistics of thendistincttype work here: It’s required to know how many unique groups of columns f1 and f2 can be. For that purpose, the following query should be used: Listing 33. The query for searching unique combinations of fields f1 and f2. ...