I am trying to write code that allows me to check if there are any cases of a particular pattern inside a table.
The way I am currently doing is with something like
select count(*)
from database.table
where column like (some pattern)
and seeing if the count is greater than 0.
I am curious to see if there is any way I can speed up this process as this type of pattern finding happens in a loop in my query and all I need to know is if there is even one such case rather than the total number of cases.
Any suggestions will be appreciated.
EDIT: I am running this inside a Teradata stored procedure for the purpose of data quality validation.
Using EXISTS will be faster if you don't actually need to know how many matches there are. Something like this would work:
IF EXISTS (
SELECT *
FROM bigTbl
WHERE label LIKE '%test%'
)
SELECT 'match'
ELSE
SELECT 'no match'
This is faster because once it finds a single match it can return a result.
If you don't need the actual count, the most efficient way in Teradata will use EXISTS:
select 1
where exists
( select *
from database.table
where column like (some pattern)
)
This will return an empty result set if the pattern doesn't exist.
In terms of performance, a better approach is to:
select the result set based on your pattern;
limit the result set's size to 1.
Check whether a result was returned.
Doing this prevents the database engine from having to do a full table scan, and the query will return as soon as the first matching record is encountered.
The actual query depends on the database you're using. In MySQL, it would look something like:
SELECT id FROM database.table WHERE column LIKE '%some pattern%' LIMIT 1;
In Oracle it would look like this:
SELECT id FROM database.table WHERE column LIKE '%some pattern%' AND ROWNUM = 1;
Related
I have been trying to find a solution for a limit-clause based on an input parameter from a Json-File. The current code looks somewhat like this
With myJsonTable (JsonText)
as (
Select JsonText)
Select * from Data
Where...
Limit
Case
WHEN (Select JSON_VALUE(JsonText, '$."Amount"') From myJsonTable is not null
THEN (Select JSON_VALUE(JsonText, '$."Amount"') From myJsonTable)
ELSE (10000000)
END
Which I cant seem to get work. The Output I am getting is
Non-negative integeter value expected in LIMIT clause
Is there a way to cast the select done? Trying different Selects anywhere in the Case clause caused the same error.
Exasol only allows constant expression in the limit clause, so it's not directly possible to specify a select statement that references myJsonTable there.
However, you can workaround this issue by using a approach similar to SQL query for top 5 results without the use of LIMIT/ROWNUM/TOP
I need dynamically obtain table name from system table and perform a select query on this table example:
SELECT "schema"+'.'+"table" FROM SVV_TABLE_INFO WHERE "table" LIKE '%blabla%'
it returns my_schema.the_main_blabla_table
And after I get this table name I need to perform :
SELECT * FROM my_schema.the_main_blabla_table LIMIT 100
Is it possible to in a single query?
If you are talking about select subquery after "from" i can say that you can do this.
You will get something like this:
SELECT * FROM
(
SELECT "schema"+'.'+"table" FROM SVV_TABLE_INFO WHERE "table" LIKE '%blabla%'
)
LIMIT 100
Unfortunately, i can't test it on yor data, but i very interested in result because i have never done something like this. If i get your question incorrect, tell me pls.
Amazon Redshift does not support the ability to take the output of a query and use it as part of another query.
Your application will need to query Redshift to obtain the relevant table name(s), then make another call to Redshift to query that table.
I have the following query. There are two possible columns that may hold the value I'm looking for, let's call them FieldA and FieldB.
If I execute this:
SELECT COUNT(1)
FROM Table
WHERE CONTAINS(Table.*, 'string')
I get back "0".
However, if I execute this:
SELECT COUNT(1)
FROM TABLE
WHERE FieldA LIKE '%string%' OR FieldB LIKE '%string%'
I get back something like 9000. I then checked and there are rows that have the word string in either FieldA.
Why does this happen? I recall that CONTAINS uses a full-text index, but I also recall that LIKE does the same, so if the problem was that the indexes are outdated, then it should fail for both of them, right?
Thanks
I believe that CONTAINS and full text searching will only yield whole word results, so you won't match the same as LIKE '%string%'. If you want to right wildcard your CONTAINS, you must write it like:
SELECT COUNT(1) FROM Table WHERE CONTAINS(Table.*, '"string*"')
However, if you want to left wildcard, you can't! You have to store a copy of your database reversed and then do:
SELECT COUNT(1) FROM Table WHERE CONTAINS(Table.*, '"gnirts*"')
https://learn.microsoft.com/en-us/previous-versions/office/developer/sharepoint-2010/ms552152(v=office.14)
How do you get leading wildcard full-text searches to work in SQL Server?
So in the example in the question, doing a CONTAINS(Table.*, 'string') is not the same as doing LIKE '%string%' and would not have the same results.
Basically I have a user table where mobile is not stored. I want to run a query to select all records starting with +91.
My current query is
Query - select count(*) from temp_table where cell_phone_no like "+91%"; Results - 0
While I know for a fact that there are certain rows with mobile numbers starting with +91.
Important: you must to know us your DBMS, because the sintax can be different, but I try to answer to your question
If you have really these rows (the row as + 91 is not good), your query can be re-write in this way:
select count(*) from temp_table where cell_phone_no like '+91%'
So, I've changed the " with a single quote '
You should check for other hidden values. I might suggest starting with this:
select cell_phone
from temp_table
where cell_phone_no like '%+%91%'
This should get any number that has a + and a 91 in it somewhere. If you get rows from this query, you need to investigate why yours doesn't work.
Is there any possibility to write delete query inside Where clause.
Example:
Select ID,Name From MyTable Where ID IN(Delete From MyTable)
It may be crazy, but let me explain my situation. In our reporting tool, we are supporting to enter SQL where query.
We will use our own Select and From Clause query and combine the user's where query input.
Example:
Select ID,Name From MyTable Where ("Query typed by user")
Here, user can type any kind of where query filter..
If he types like ID=100 our final query becomes like this
Select ID,Name From MyTable Where (ID=100)
One of our customer asked us what will happen if anyone type the delete query as where query filter. he feels this may be the security hole..so we have tried that kind of possibility in our dev environment. But the sql returns error for the following query.
Select ID,Name From MyTable Where ID IN(Delete From MyTable)
So finally, my question is, is there any other possibility to write Delete Query inside Where clause or Select clause.. If it possible, how can I restrict it?
Yes. They can run a delete. They can type:
1 = 1; DELETE FROM MY_TABLE;
Or even worse in some ways, (since you should have backups):
1 = 0 UNION SELECT SOCIAL_SECURITY_NUMBER, CREDIT_CARD_NUMBER, OTHER_SENSITIVE_DATA FROM MY_SENSITIVE_TABLE;
Now, in your case its hard to validate. Normally if you are just passing a value to filter on you can use parameterised sql to save yourself. You however also need to let the user select a column. In cases like these, usually we use a drop down to allow the user to select a predefined list of columns and then validate the column name server side. We give the user a text box to enter the value to match and then parameterise that.
It's not quite possible. But he can do something like this :
Select ID,Name From MyTable Where (ID=100); (DELETE FROM MyTable Where 1 = 1)
by using ID=100); (DELETE FROM MyTable Where 1 = 1 instead of ID=100
I believe what your customer is talking about is SQL injection, as long as you have taken appropriate methods to block other queries from running after your select statement is done, then you should have no problem in letting them type whatever it is that you want.
From my experience there is no way to delete anything when you are doing a select statement.
Just make sure you have query terminator characters so they don't write something like the following.
select column1,column2, from myTable where ID in (1,2); delete from my table
this would be a valid worry from your customer if you aren't taking proper steps to prevent sql injection from happening.
You could have your SQL reporting tool just not have update, or delete permission and just have it have Read permission. However, it is up to you guys have you handle your sql injection security.