Here again, the result row ordering might vary. You can request that duplicate rows be removed from the result of a query:
But you'd always get the results shown above if you do: In this example, the sort order isn't fully specified, and so you might get the San Francisco rows in either order. You can request that the results of a query be returned in sorted order: WHERE city = 'San Francisco' AND prcp > 0.0 For example, the following retrieves the weather of San Francisco on rainy days: The usual Boolean operators ( AND, OR, and NOT) are allowed in the qualification. These variables can be set using the SET statement, by editing the nf configuration file, through the PGOPTIONS environmental variable (when using libpq or a libpq -based application), or through command-line flags when starting the postgres server. The WHERE clause contains a Boolean (truth value) expression, and only rows for which the Boolean expression is true are returned. SHOW will display the current setting of run-time parameters. (The AS clause is optional.)Ī query can be “ qualified” by adding a WHERE clause that specifies which rows are wanted. Another way to show tables in PostgreSQL is to use the SELECT statement to query data from the PostgreSQL catalog as follows: Syntax: SELECT FROM pgcatalog.
Notice how the AS clause is used to relabel the output column. SELECT city, (temp_hi+temp_lo)/2 AS temp_avg, date FROM weather You can write expressions, not just simple column references, in the select list. SELECT city, temp_lo, temp_hi, prcp, date FROM weather Here * is a shorthand for “ all columns”. For example, to retrieve all the rows of table weather, type: The statement is divided into a select list (the part that lists the columns to be returned), a table list (the part that lists the tables from which to retrieve the data), and an optional qualification (the part that specifies any restrictions). An SQL SELECT statement is used to do this. An SQL SELECT statement is used to do this. To retrieve data from a table, the table is queried.
To retrieve data from a table, the table is queried.
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