Help Center/ GaussDB/ Developer Guide(Distributed_8.x)/ Application Development Guide/ Development Based on libpq/ libpq Interface Reference/ Database Statement Execution Functions/ PQprepare
Updated on 2024-08-20 GMT+08:00
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PQprepare

Description

Commits a request to create a prepared statement with given parameters and waits for completion.

Prototype

PGresult* PQprepare(PGconn* conn, const char* stmtName, const char* query, int nParams, const Oid* paramTypes);

Parameters

Table 1 PQprepare parameters

Keyword

Description

conn

Object pointer that contains the connection information.

stmtName

Prepared statement to be executed.

query

Query string to be executed.

nParams

Parameter quantity.

paramTypes

Array of the parameter type.

Return Values

PGresult indicates the object pointer that contains the query result.

Precautions

  • PQprepare creates a prepared statement for later execution with PQexecPrepared. This function allows commands to be repeatedly executed, without being parsed and planned each time they are executed. PQprepare is supported only in protocol 3.0 or later. It will fail when protocol 2.0 is used.
  • This function creates a prepared statement named stmtName from the query string, which must contain an SQL command. stmtName can be "" to create an unnamed statement. In this case, any pre-existing unnamed statement will be automatically replaced. Otherwise, this is an error if the statement name has been defined in the current session. If any parameters are used, they are referred to in the query as $1, $2, and so on. nParams is the number of parameters for which types are pre-specified in the array paramTypes[]. (The array pointer can be NULL when nParams is 0.) paramTypes[] specifies the data types to be assigned to the parameter symbols by OID. If paramTypes is NULL, or any element in the array is 0, the server assigns a data type to the parameter symbol in the same way as it does for an untyped literal string. In addition, the query can use parameter symbols whose numbers are greater than nParams. Data types of these symbols will also be inferred.

You can also execute the SQLPREPARE statement to create a prepared statement that is used with PQexecPrepared. Although there is no libpq function of deleting a prepared statement, the SQL DEALLOCATE statement can be used for this purpose.

Examples

For details, see Examples.