This section describes functions and operators for examining and manipulating bit strings, that is values of the types bit and bit varying. Aside from the usual comparison operators, the operators shown in Table 9-13 can be used. Bit string operands of &, |, and # must be of equal length. When bit shifting, the original length of the string is preserved, as shown in the examples. Table 9-13. Bit String Operators Operator Description Example Result || concatenation B'10001' || B'011' 10001

Because each worker executes the parallel portion of the plan to completion, it is not possible to simply take an ordinary query plan and run it using multiple workers. Each worker would produce a full copy of the output result set, so the query would not run any faster than normal but would produce incorrect results. Instead, the parallel portion of the plan must be what is known internally to the query optimizer as a partial plan; that is, it must constructed so that each process will which e

The INSERT statement is used to populate a table with rows: INSERT INTO weather VALUES ('San Francisco', 46, 50, 0.25, '1994-11-27'); Note that all data types use rather obvious input formats. Constants that are not simple numeric values usually must be surrounded by single quotes ('), as in the example. The date type is actually quite flexible in what it accepts, but for this tutorial we will stick to the unambiguous format shown here. The point type requires a coordinate pair as input, as s

Error, warning, and log messages generated within the server code should be created using ereport, or its older cousin elog. The use of this function is complex enough to require some explanation. There are two required elements for every message: a severity level (ranging from DEBUG to PANIC) and a primary message text. In addition there are optional elements, the most common of which is an error identifier code that follows the SQL spec's SQLSTATE conventions. ereport itself is just a shell f

Every table has several system columns that are implicitly defined by the system. Therefore, these names cannot be used as names of user-defined columns. (Note that these restrictions are separate from whether the name is a key word or not; quoting a name will not allow you to escape these restrictions.) You do not really need to be concerned about these columns; just know they exist. oid The object identifier (object ID) of a row. This column is only present if the table was created using WI

NameCREATE RULE -- define a new rewrite rule Synopsis CREATE [ OR REPLACE ] RULE name AS ON event TO table_name [ WHERE condition ] DO [ ALSO | INSTEAD ] { NOTHING | command | ( command ; command ... ) } where event can be one of: SELECT | INSERT | UPDATE | DELETE Description CREATE RULE defines a new rule applying to a specified table or view. CREATE OR REPLACE RULE will either create a new rule, or replace an existing rule of the same name for the same table. The Postg

NameSET TRANSACTION -- set the characteristics of the current transaction Synopsis SET TRANSACTION transaction_mode [, ...] SET TRANSACTION SNAPSHOT snapshot_id SET SESSION CHARACTERISTICS AS TRANSACTION transaction_mode [, ...] where transaction_mode is one of: ISOLATION LEVEL { SERIALIZABLE | REPEATABLE READ | READ COMMITTED | READ UNCOMMITTED } READ WRITE | READ ONLY [ NOT ] DEFERRABLE Description The SET TRANSACTION command sets the characteristics of the current tra

Transactions are a fundamental concept of all database systems. The essential point of a transaction is that it bundles multiple steps into a single, all-or-nothing operation. The intermediate states between the steps are not visible to other concurrent transactions, and if some failure occurs that prevents the transaction from completing, then none of the steps affect the database at all. For example, consider a bank database that contains balances for various customer accounts, as well as tot

A window function performs a calculation across a set of table rows that are somehow related to the current row. This is comparable to the type of calculation that can be done with an aggregate function. But unlike regular aggregate functions, use of a window function does not cause rows to become grouped into a single output row — the rows retain their separate identities. Behind the scenes, the window function is able to access more than just the current row of the query result. Here is an ex

The examples in the previous section illustrated full text matching using simple constant strings. This section shows how to search table data, optionally using indexes. 12.2.1. Searching a Table It is possible to do a full text search without an index. A simple query to print the title of each row that contains the word friend in its body field is: SELECT title FROM pgweb WHERE to_tsvector('english', body) @@ to_tsquery('english', 'friend'); This will also find related words such as friends