传送给数据库的 SQL 语句通过一个包含两个步骤的过程来返回结果。首先准备它们，然后处理它们。借助 Statement 对象，这两个阶段对应用程序而言变成一个阶段。
PreparedStatement 允许将这两个步骤分开。准备步骤在创建对象时发生，而处理步骤在对 PreparedStatement 对象调用 executeQuery、executeUpdate 或 execute 方法时发生。
prepareStatement
PreparedStatement prepareStatement(String sql,
int autoGeneratedKeys)
throws SQLException
Creates a default PreparedStatement object that has the capability to retrieve auto-generated keys. The given constant tells the driver whether it should make auto-generated keys available for retrieval. This parameter is ignored if the SQL statement is not an INSERT statement, or an SQL statement able to return auto-generated keys (the list of such statements is vendor-specific).
Note: This method is optimized for handling parametric SQL statements that benefit from precompilation. If the driver supports precompilation, the method prepareStatement will send the statement to the database for precompilation. Some drivers may not support precompilation. In this case, the statement may not be sent to the database until the PreparedStatement object is executed. This has no direct effect on users; however, it does affect which methods throw certain SQLExceptions.
Result sets created using the returned PreparedStatement object will by default be type TYPE_FORWARD_ONLY and have a concurrency level of CONCUR_READ_ONLY. The holdability of the created result sets can be determined by calling getHoldability().
Parameters:
sql - an SQL statement that may contain one or more '?' IN parameter placeholders
autoGeneratedKeys - a flag indicating whether auto-generated keys should be returned; one of Statement.RETURN_GENERATED_KEYS or Statement.NO_GENERATED_KEYS
Returns:
a new PreparedStatement object, containing the pre-compiled SQL statement, that will have the capability of returning auto-generated keys
Throws:
SQLException - if a database access error occurs, this method is called on a closed connection or the given parameter is not a Statement constant indicating whether auto-generated keys should be returned
SQLFeatureNotSupportedException - if the JDBC driver does not support this method with a constant of Statement.RETURN_GENERATED_KEYS
Since:
1.4
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prepareStatement
PreparedStatement prepareStatement(String sql,
int[] columnIndexes)
throws SQLException
Creates a default PreparedStatement object capable of returning the auto-generated keys designated by the given array. This array contains the indexes of the columns in the target table that contain the auto-generated keys that should be made available. The driver will ignore the array if the SQL statement is not an INSERT statement, or an SQL statement able to return auto-generated keys (the list of such statements is vendor-specific).
An SQL statement with or without IN parameters can be pre-compiled and stored in a PreparedStatement object. This object can then be used to efficiently execute this statement multiple times.
Note: This method is optimized for handling parametric SQL statements that benefit from precompilation. If the driver supports precompilation, the method prepareStatement will send the statement to the database for precompilation. Some drivers may not support precompilation. In this case, the statement may not be sent to the database until the PreparedStatement object is executed. This has no direct effect on users; however, it does affect which methods throw certain SQLExceptions.
Result sets created using the returned PreparedStatement object will by default be type TYPE_FORWARD_ONLY and have a concurrency level of CONCUR_READ_ONLY. The holdability of the created result sets can be determined by calling getHoldability().
Parameters:
sql - an SQL statement that may contain one or more '?' IN parameter placeholders
columnIndexes - an array of column indexes indicating the columns that should be returned from the inserted row or rows
Returns:
a new PreparedStatement object, containing the pre-compiled statement, that is capable of returning the auto-generated keys designated by the given array of column indexes
Throws:
SQLException - if a database access error occurs or this method is called on a closed connection
SQLFeatureNotSupportedException - if the JDBC driver does not support this method
Since:
1.4
----------------------------------------------------------------------
prepareStatement
PreparedStatement prepareStatement(String sql,
String[] columnNames)
throws SQLException
Creates a default PreparedStatement object capable of returning the auto-generated keys designated by the given array. This array contains the names of the columns in the target table that contain the auto-generated keys that should be returned. The driver will ignore the array if the SQL statement is not an INSERT statement, or an SQL statement able to return auto-generated keys (the list of such statements is vendor-specific).
An SQL statement with or without IN parameters can be pre-compiled and stored in a PreparedStatement object. This object can then be used to efficiently execute this statement multiple times.
Note: This method is optimized for handling parametric SQL statements that benefit from precompilation. If the driver supports precompilation, the method prepareStatement will send the statement to the database for precompilation. Some drivers may not support precompilation. In this case, the statement may not be sent to the database until the PreparedStatement object is executed. This has no direct effect on users; however, it does affect which methods throw certain SQLExceptions.
Result sets created using the returned PreparedStatement object will by default be type TYPE_FORWARD_ONLY and have a concurrency level of CONCUR_READ_ONLY. The holdability of the created result sets can be determined by calling getHoldability().
Parameters:
sql - an SQL statement that may contain one or more '?' IN parameter placeholders
columnNames - an array of column names indicating the columns that should be returned from the inserted row or rows
Returns:
a new PreparedStatement object, containing the pre-compiled statement, that is capable of returning the auto-generated keys designated by the given array of column names
Throws:
SQLException - if a database access error occurs or this method is called on a closed connection
SQLFeatureNotSupportedException - if the JDBC driver does not support this method
Since:
1.4
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