I'm writing a simple database migration code in clojure using the new seancorfield/next.jdbc library.
How do I execute several SQL statements at once? The usecase is that I have a SQL file containing query code for migrating from one version to the next. next.jdbc/execute! only executes one statement as designed.
Whether you can execute multiple statements in a single JDBC operation is database-dependent. Some databases allow multiple statements in a single operation, separated by a semicolon. If the JDBC driver supports it, next.jdbc will also support it.
If your JDBC driver does not support it, you'll need to make multiple execute! calls. Some databases allow you to wrap multiple DDL operations in a transaction (some of them ignore the transaction and commit each DDL operation separately anyway), some databases explicitly disallow a transaction around DDL operations.
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The tkprof utility generates the trace file with three types of information which are Parse, Execute and Fetch. Could you please explain what is the difference between these three? What will be counted as Parse and Execute and Fetch?
Thanks in advance for your help.
When you issue a SQL statement, Oracle:
Parses your SQL statement. That means Oracle analyzes the correctness of the syntax, checks the access rights, and creates the execution plan (or takes it from the cache).
Actually executes your SQL statement.
For SELECT statements, Oracle fetches the rows returned by your query. (For INSERT, DELETE, and UPDATE Oracle fetches nothing).
The numbers of these operations is written in the trace.
If we are talking about the performance tuning, the idea is to parse SQL statements once and then keep them in cache, execute them when you need and do not close cursors if you will need them again to reduce number of fetches.
I am not sure in case of Stored Procedures, if Postgresql treats static sql any differently from a query submitted as a quoted string.
When I create a stored procedure in PostgreSQL using static sql, there seems to be no validation of the table names and table columns or column types but when I run the procedure I get the listing of the problems if any.
open ref_cursor_variable for
select usr_name from usres_master;
-- This is a typing mistake. The table name should be users_master. But the stored procedure is created and the error is thrown only when I run the procedure.
When I run the procedure I (naturally) get some error like :
table usres_master - invalid table name
The above is a trivial version. The real procedures we use at work combine several tables and run to at least a few hundred lines. In PostgresQL stored procedure, is there no advantage to using static sql over dynamic sql i.e. something like open ref_cursor_variable for EXECUTE select_query_string_variable.
The static SQL should be preferred almost time - dynamic SQL should be used only when it is necessary
from performance reasons (dynamic SQL doesn't reuse execution plans). One shot plan can be better some times (and necessary).
can reduce lot of code
In other cases uses static SQL every time. Benefits:
readability
reuse of execution plans
it is safe against SQL injection by default
static check is available
The source of a function is just a string to Postgres. The main reason for this is the fact that Postgres (unlike other DBMS) supports many, even installable languages for functions and procedures. As the Postgres core can't possibly know the syntax of all languages, it can not validate the "inner" part of a function. To my knowledge the "language API" does not contain any "validate" method (in theory this would probably be possible though).
If you want to statically validate your PL/pgSQL functions (and procedures since Postgres 11) you could use e.g. https://github.com/okbob/plpgsql_check/
I just created a stored procedure in MS SQL DB using TOAD.
what it does is that it accepts an ID wherein some records are associated with, then it inserts those records to a table.
next part of the stored procedure is to use the ID input to search on the table where the items got inserted and then return it as the result set to the user just to confirm that the information got inserted.
IN TOAD, it does what is expected. It inserts date and returns information using just the stored procedure.
IN Oracle SQL developer however, it does the insert and it ends at that. It seems to not execute the 2nd part of the stored procedure which is a select stmt.
I just have a feeling that this is because of the jdbc adapter. Also why I'm asking is because I'm using a reporting tool Pentaho Report Designer and it would really make it easier if I can do 2 things at the same time. Pentaho Report Designer is also using jdbc adapters, not a coincidence maybe?
But if there are other things that I can tweak I'd really appreciate it.
This is a guess, but worth considering...
There are things called "Batches", where are sets of SQL Statements that are all sent to the server at once, and executed by the server as one set of statements, within a single server-side session. Sending a set of sql statements to the server as a batch will often result in different results than if you sent them one at a time, where each statement is executed in its own session.
I haven't used Toad (or Oracle) in a while, but as I recall, it dealt with batches differently than the other ide I used. If the second statement in your set is relying on being in the same session as the first, and in one ide it is in a separate session, then this might explain what is happening.
select max(Key) from MyTable with(nolock)
I have this T-SQL statement but need to use one statement for both SQL Server and Oracle as well, of course the “with (nolock)” is not recognised by Oracle. Is there a way having this statement that will run on both databases. By either an Oracle ignoring the “with (nolock)” or only Sqlserver using this part of the statement or a way or coded that both with understand.
The reason why I am using No lock is because multiple users are accessing the same table and I need to find the max value during the transactions.
Oracle does things a bit differently so I do not have to worry about table locks.
Your queries are doing different things. What are the semantics of the query supposed to be? Is it supposed to return max(Key) including the effect of uncommitted transactions as your SQL Server version indicates? If so
SET TRANSACTION ISOLATION LEVEL READ UNCOMMITTED;
select max(Key)
from MyTable;
Is the same semantics. The syntax should work fine on both AFAIK.
If instead you want the last committed max(Key) you would need to change the SQL Server database to use read committed snapshot isolation by default so it behaves more similarly to Oracle. Or alternatively you could achieve similar semantics with ROWLOCK,READPAST hints but then you are back to needing two different queries.
does statement object contain the session id the database returns for the current session? What does a resultset
contain?
To the best of my knowledge, no, Statements do not have session IDs. It seems like the Java API specifications for the Statement class backs that up. Basically, Statements are used to execute SQL statements by specifying a SQL query through the execute method.
A ResultSet is used to retrieve results which are returned by executing a query via a Statement or PreparedStatement.
The JDBC(TM) Database Access trail of The Java Tutorials contains some information on these topics. The following sections may be of interest:
Lesson: JDBC Basics
Updating Tables
Retrieving Values from Result Sets