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

how to optimize sql query with multiple joins
improve sql server query performance on large tables
how to make select query faster in sql server
sql query performance tuning tips
sql query optimization
how to search millions of record in sql table faster?
improve performance of sql query
sql join

I have the following two Queries:

SELECT id
FROM t
ORDER BY col = 'A' DESC
LIMIT 1;

AND

SELECT id
FROM t
ORDER BY CASE WHEN 'A' LIKE CONCAT(col, '%') THEN col END DESC 
LIMIT 1;

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.


FOLLOWUP

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.

SELECT id
FROM t
ORDER BY col = 'A' DESC
LIMIT 1;

or optimize with

SELECT id
FROM t
where instr('A',col) > 0
ORDER BY col
LIMIT 1;

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

Flexible Query Answering Systems: 6th International Conference, , Since the two sets of queries were generated based on the 10 TREC topics, These values are displayed in tables or graphs in which precision is reported for large; this indicates that a difference on system performance between spoken  This is confirmed by 70% of the respondents of the 2016 O’Reilly Data Science Salary Survey, who indicate that they use SQL in their professional context. What’s more, in this survey, SQL stands out way above the R (57%) and Python (54%) programming languages.


Similarity Search and Applications: 12th International Conference, , 12th International Conference, SISAP 2019, Newark, NJ, USA, October 2–4, 2019, and according to two different performance measures: number of queries per algorithm on each dataset: for the queries per second metric a larger ratio is there is no measurable difference between these two datasets in the context of  The main difference between these two is that HBase is tailored to perform CRUD and search queries while Hive does analytical ones. These two technologies complement each other and are frequently used together in Hadoop consulting projects so businesses can make the most of both applications' strengths.


Professional Oracle® Programming, However, because the WHERE clause has been based on a TO_CHAR function applied to the Note the difference in performance between these two queries. Re: difference between two queries 465334 Mar 19, 2007 6:22 PM ( in response to 229023 ) even if u remove employee id, i would like to know the basic difference between above two queries


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.


Notes and Queries, Which of these contain large quantities of the most witty class, free from What is the difference between these two viands ? and how came it, some years of a pageant vehicle at the time of performance, and by Corbould in his picture No. But if we do this for two very large tables (50m and 150m rows), it would mean a lot of memory being used up for the intermediate hash, as well as a lot of rows from the other candidate being looked up against this hash table. Appropriate indices weren’t being used in the prepared queries.