Prepared_statement: a statement that can contain placeholders.
| bool Prepared_statement::execute_loop |
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String * |
expanded_query, |
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bool |
open_cursor |
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) |
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Execute a prepared statement.
Re-prepare it a limited number of times if necessary.
Try to execute a prepared statement. If there is a metadata validation error, prepare a new copy of the prepared statement, swap the old and the new statements, and try again. If there is a validation error again, repeat the above, but perform no more than MAX_REPREPARE_ATTEMPTS.
- Note
- We have to try several times in a loop since we release metadata locks on tables after prepared statement prepare. Therefore, a DDL statement may sneak in between prepare and execute of a new statement. If this happens repeatedly more than MAX_REPREPARE_ATTEMPTS times, we give up.
- Parameters
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| expanded_query | Query string. |
| open_cursor | Flag to specift if a cursor should be used. |
- Returns
- a bool value representing the function execution status.
- Return values
-
| true | error: either MAX_REPREPARE_ATTEMPTS has been reached, or some general error |
| false | successfully executed the statement, perhaps after having reprepared it a few times. |
Routines to assign parameters from data supplied by the client.
Update the parameter markers by reading data from the packet and and generate a valid query for logging.
- Note
- with_log is set when one of slow or general logs are open. Logging of prepared statements in all cases is performed by means of regular queries: if parameter data was supplied from C API, each placeholder in the query is replaced with its actual value; if we're logging a [Dynamic] SQL prepared statement, parameter markers are replaced with variable names. Example:
mysqld_stmt_prepare("UPDATE t1 SET a=a*1.25 WHERE a=?")
--> general logs gets [Prepare] UPDATE t1 SET a*1.25 WHERE a=?"
mysqld_stmt_execute(stmt);
--> general and binary logs get
[Execute] UPDATE t1 SET a*1.25 WHERE a=1"
If a statement has been prepared using SQL syntax:
PREPARE stmt FROM "UPDATE t1 SET a=a*1.25 WHERE a=?"
--> general log gets
[Query] PREPARE stmt FROM "UPDATE ..."
EXECUTE stmt USING @a
--> general log gets
[Query] EXECUTE stmt USING @a;- Return values
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| bool Prepared_statement::prepare |
( |
const char * |
query_str, |
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size_t |
query_length |
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) |
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Parse statement text, validate the statement, and prepare it for execution.
You should not change global THD state in this function, if at all possible: it may be called from any context, e.g. when executing a COM_* command, and SQLCOM_* command, or a stored procedure.
- Parameters
-
| query_str | statement text |
| query_length | the length of the statement text |
- Note
- Precondition: The caller must ensure that thd->change_list and thd->item_list is empty: this function will not back them up but will free in the end of its execution.
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Postcondition: thd->mem_root contains unused memory allocated during validation.
| bool Prepared_statement::reprepare |
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| ) |
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private |
Reprepare this prepared statement.
Performs a light reset of the Prepared_statement object (resets its MEM_ROOT and clears its MEM_ROOT allocated members), and calls prepare() on it again.
The resetting of the MEM_ROOT and clearing of the MEM_ROOT allocated members is performed by a swap operation (swap_prepared_statement()) on this Prepared_statement and a newly created, intermediate Prepared_statement. This both clears the data from this object and stores a backup of the original data in the intermediate object. If the repreparation fails, the original data is swapped back into this Prepared_statement.
- Return values
-
| true | an error occurred. Possible errors include incompatibility of new and old result set metadata |
| false | success, the statement has been reprepared |
Swap the MEM_ROOT allocated data of two prepared statements.
This is a private helper that is used as part of statement reprepare. It is used in the beginning of reprepare() to clear the MEM_ROOT of the statement before the new preparation, while keeping the data available as some of it is needed later in the repreparation. It is also used for restoring the original data from the copy, should the repreparation fail.
The operation is symmetric. It can be used both for saving an original statement into a backup, and for restoring the original state of the statement from the backup.
Validate statement result set metadata (if the statement returns a result set).
Currently we only check that the number of columns of the result set did not change. This is a helper method used during re-prepare.
- Parameters
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| [in] | copy | the re-prepared prepared statement to verify the metadata of |
- Return values
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| true | error, ER_PS_REBIND is reported |
| false | statement return no or compatible metadata |
If this is an SQL prepared statement or EXPLAIN, return false – the metadata of the original SELECT, if any, has not been sent to the client.
Column counts mismatch, update the client
Name of the current (default) database.
If there is the current (default) database, "db" contains its name. If there is no current (default) database, "db" is NULL and "db_length" is 0. In other words, "db", "db_length" must either be NULL, or contain a valid database name.
- Note
- this attribute is set and alloced by the slave SQL thread (for the THD of that thread); that thread is (and must remain, for now) the only responsible for freeing this member.
1.8.13