I'm rather new at database management, so this might not be feasible, but I got a handful of SQL select queries, rather long ones at that. What I'd like is to get the table column names and structure, without access to the actual database, so as to get a map of all this queries.
context: All we have are the queries used to output tables that will be given to us latter.
This need not be done with actual SQL code, maybe a short script in other language or a utility somebody knows of (but I do have MySQL workbench)
You can add a CREATE TABLE statement in front of your select queries to get the column names.
You cannot infer data types or keys from select queries.
For column names do something like:
drop table if exists your_table_name;
create table your_table_name
select *
from ...
where the select * portion is replaced by the select queries you have.
Then to see the column names in a friendlier way you can do:
show create table your_table_name;
or
desc your_table_name;
Related
I have a large (1000s) list of IDs in a text file. I want to return the rows from my database that correspond to these IDs. How can I do this?
My current method is to simply paste the whole list into a gigantic SQL query and run that. It works, but I feel like there must be a better way.
As the list of values goes bigger and bigger, a better solution is to load it into a table, that you can then use it your query. In MySQL, the load data statement syntax comes handy for this.
Consider something like:
create temporary table all_ids (id int);
load data infile 'myfile.txt' into table all_ids;
create index idx_all_ids on all_ids(id); -- for performance
select t.*
from mytable t
where exists (select 1 from all_ids a where a.id = t.id)
The load data syntax accepts many options to accommodate the format of the input file - you can read the documentation for more information.
I'd like to know if it is possible to create an SQL function that will automatically update my View and add to it new tables in my DB.
My DB consist of multiple tables (same data structure) and are named as follow "MM_DD", now I would like to create a VIEW that joins all this data ( pretty simple , see query below) but I wish to automate the process so every time a new table is added the view will update.
CREATE OR REPLACE VIEW `viewTable` AS
select *,
md5(CONCAT(`columnA`,`columnB`)) AS myPK_id
from `05_06`
union all
select *,
md5(CONCAT(`columnA`,`columnB`)) AS myPK_id
from `05_08`
ect...
What I am doing at the moment is using PHP every time a table is added. It loops through the tables and create / update the view.
select * from information_schema.tables WHERE table_name LIKE '%05%'
Now that I have an array of table names -> create my Query string -> replace view...
Is this possible to do this in SQL?
If so, what is the correct approach?
Write a stored procedure to rebuild your view. You'll need to use what MySQL internally calls "prepared statements" so you can use string manipulation.
You'll still use your SELECT ... FROM information_schema.tables query to drive this stored procedure.
Once you get this working, you can embed it in a mySQL event, and arrange to run it automatically. For example, you could run it at the same time late at night.
Or, you can invoke the stored procedure immediately after you create one of these tables.
I was wondering is there a performance difference between:
query 1: CREATE TEMPORARY TABLE temp_table1 AS SELECT * FROM lookup_table JOIN ...
then
INSERT INTO dest_table SELECT * FROM temp_table1
vs
query 2: INSERT INTO dest_table SELECT * FROM lookup_table JOIN ...
My concern was, the lookup_table is accessed very often by different users and when I run query 2, most of the users need to wait longer to be able to retrieve their result. What I was thinking was to write the data into a temporary table then write it to dest_table afterwards . Im just not sure if writing into a temp table with give a difference performance compared to writing it directly to the destination table. Im using mysql 5.6.
The reason why I need to write data from lookup_table to dest_table is because I need to create a report from it. Seeing how complex the query from lookup_table is makes it very difficult to create a report so I decided to move those data to a single table then just make a report from it.
You're concerned about the lockout time that's taken by the SELECT query that populates this temporary table.
The tables are implemented the same way, so the cost of creating will be very close to the same in either case.
You might be able to get it to go a little faster by creating your temporary table in the MEMORY access method, but I suspect the difference will be minimal; the work involved here is the SELECT / JOIN stuff.
You might be able to get it to go faster by making sure your target table has no indexes when you create it. CREATE ... AS SELECT will do that.
You will be able to make it cheaper to create by getting rid of SELECT * (which yields redundant columns on JOINs anywhow), and instead specify the columns you really need.
But, your best bet is to figure out why you're creating this table, and see if you can deliver on those requirements by writing queries against the source tables instead. If you make those query operations efficient, you've saved yourself lots of data shuffling.
CONTEXT:
we have big databases with loads of tables. Most of them (99%) are using innodb.
we want to have a daily process that monitors which table has been modified. As they use innodb the value of Update_time from
SHOW table STATUS from information_schema;
is null.
For that reason we want to create a daily procedure that will store the checksum (and other stuffs for that matters) of each table somewhere (preferably another table). On that, we will do different checks.
PROBLEM:
I'm trying to use
checksum table from db_schema.table_name;
which returns a resultset-table with 2 columns: "table","checksum".
It gives me the value I want but I'm not able to use it in a select or insert statement.
I tried a lot of things like:
select `checksum` from (checksum table from db_schema.table_name);
or other similar queries. But I'm not able to extract the data from the resultset.
Is there a way I can do that?
Thanks in advance for your help.
EDIT: in the end what I want is to build a more complex resultset having different informations in it (table schema, table name, count, checksum, datetime:now()...)
Then I'll use this resultset to compare with the values of yesterday and draw my own statistics. That's why I want to get the checksum from that resultset.
There is no possibility to save the result of CHECKSUM TABLE directly using SQL. Neither can you use prepared statements or cursors in stored procedures to use the checksum result.
You best make a script around it, or download some popular tools doing it for you.
For MyISAM tables using the CHECKSUM=1 table argument, you can simply use INFORMATION_SCHEMA like this:
SELECT TABLE_NAME,CHECKSUM FROM INFORMATION_SCHEMA.TABLES
WHERE TABLE_SCHEMA = 'test' AND ENGINE='MyISAM'
AND CHECKSUM IS NOT NULL;
Is it possible to use the create table query (create table t2 like t1) to get the query instead the actual table? Kind of like duplicating some management consoles Send To editor feature?
I think you're looking for SHOW CREATE TABLE tablename;
'tablename' can be the table within the current database, if you've selected one, or you can qualify it as in 'dbname.tablename'. The output can be used to create the table again. In fact, I sometimes use it in scripts that need to either use an existing table or create it if it doesn't exist. First I'll get the table creation info as shown above, and then I'll use something like"
CREATE TABLE IF NOT EXISTS tablename .........
Where '..........' is all the goodies that SHOW CREATE TABLE tablename gives me.
If you're interested in a good tutorial on MySQL (the database), as well as SQL (the language), you might have a look at the O'Reilly book, Learning MySQL. It's pretty good.