How big is the difference in performance between these two Queries?

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I have the following two Queries:




The Two gives the same result with and without the LIMIT 1, What is the difference between those two Queries in Performance? The 2nd Query is useful with multiple word But with a single-word both Queries does the same effect on the ORDER.

Is there any difference That it is better If I used the 1st Query for Single-Word If I could?

I don't expect any measurable difference in performance. This is a full scan of all rows in t, to retrieve the columns id and col. (This could be a scan of the table, or a covering index.)

The ORDER BY can't be satisfied from an index; either way, we're going to be seeing a "Using filesort" operation in the EXPLAIN output.

The equality comparison may be marginally less work than the CONCAT and LIKE comparison.

But the queries are significantly different.

The CASE expression is returning values of col or NULL. The query ordering the result of an equality comparison is returning 1, 0 or NULL.

There might be a difference in the performance of the sort operation, one is sorting integers, the second is sorting whatever datatype col is.

With trivial sets, no measurable difference in performance.

With huge sets, both queries may have horrendous performance.

I suspect a different query would satisfy the specification much more efficiently than either of the options.

But why do we need an ORDER BY at all? There's a LIMIT 1. So we're returning an id value. That could be from a row with col='A', or not.

Before we get too worked up about which is faster, we should make sure we are satisfying the specification.

I strongly suspect that the spec could be tweaked to entirely avoid a potentially expensive sort operation, to return just one id value.


The specification that this query satisfies isn't clear; the reason for running this query.

Why are we returning just one id value? We are wanting to return an id value of a row that "matches" a string. And if there isn't a row that matches, then return the id of a row in the table with a non-NULL col value. And if there isn't a row with a non-NULL col value, then return id of any row in the table.

(The first query in the question is different from the second, in regards to case 2 and 3... the row that gets returned in the case of no matching col values, NULL vs non-NULL.)

Data Warehousing for Biomedical Informatics, just enough data to be able to notice the performance differences between the If the connection between those two queries is made in the application layer, Some tools include settings that determine when and where different aspects of  WHERE ModifiedDate BETWEEN '2000-01-01' and '2000-01-31'; 1. Highlight and run queries 1 and 2. Explain why there is no difference in performance between the two queries. Query 1 uses an index to perform an index seek on the LastName column to find the rows. Since

This simple structure should suffice. You don't need to complicate stuff.

Problem with this statement, without the where clause is that you are returning all rows and then cutting the result to 1.. which means 1 million rows to read but get the first one.


or optimize with

where instr('A',col) > 0

Will get the matching rows but return only 1 row. so from 1 million rows, 300 rows where matched then get the 1st one.

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More efficient SQL with query planning and optimization (article , SELECT * FROM books WHERE author = "J K Rowling";. For this query, these are 2 different ways that SQL could find the results: Do a "full optimizations (​improvements that always result in better performance, like simplifying 5*10 into 50). As many of my tips deal with SQL Server performance we will test the performance of these two datatypes by running through a simple test case to see if we can measure any significant performance differences. We will setup two almost identical tables with the only variance being the datatype of the primary key column.

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