Difference between revisions of "String over columns"
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| − | + | Normally a string can be searched for across many columns using the <code>OR</code> function but this is not efficient as this could lead to errors while using | |
| + | a <code>CONCAT</code> function ( || for oracle, + for sqlserver) could do the same task but can get rid of the risk of errors | ||
<div class='ht'> | <div class='ht'> | ||
<div class=params>schema:scott</div> | <div class=params>schema:scott</div> | ||
| Line 15: | Line 16: | ||
<div> | <div> | ||
SELECT name FROM bedrooms | SELECT name FROM bedrooms | ||
| − | + | WHERE floorcolor = 'YELLOW' | |
| − | + | OR ceilingcolor = 'YELLOW' | |
| − | + | OR wallcolor = 'YELLOW' | |
<p>Using <code>OR</code> increases the chances for careless mistakes instead | <p>Using <code>OR</code> increases the chances for careless mistakes instead | ||
<code>CONCAT</code> could be used to make the query more efficient.</p> | <code>CONCAT</code> could be used to make the query more efficient.</p> | ||
| Line 24: | Line 25: | ||
COALESCE(floorcolor,' '). | COALESCE(floorcolor,' '). | ||
</div> | </div> | ||
| − | <source lang='sql' class='def'>SELECT name FROM bedrooms | + | <source lang='sql' class='def e-oracle'> |
| − | WHERE CONCAT (':',floorcolor,':',ceilingcolor,':',wallcolor,':') | + | SELECT name FROM bedrooms |
| − | LIKE '%:YELLOW:%'</source> | + | WHERE ':' || floorcolor || ':' || ceilingcolor || ':' || wallcolor || ':' |
| + | LIKE '%:YELLOW:%'</source> | ||
| + | <source lang='sql' class='def e-sqlserver'> | ||
| + | SELECT name FROM bedrooms | ||
| + | WHERE ':' + floorcolor + ':' + ceilingcolor + ':' + wallcolor + ':' | ||
| + | LIKE '%:YELLOW:%'</source> | ||
| + | <source lang='sql' class='def'> | ||
| + | SELECT name FROM bedrooms | ||
| + | WHERE CONCAT (':',floorcolor,':',ceilingcolor,':',wallcolor,':') | ||
| + | LIKE '%:YELLOW:%'</source> | ||
<div class="ecomm e-mysql" style="display: none">Instead of <code>COALESCE</code> or <code>NVL</code>, <code>IFNULL</code> can be used.</div> | <div class="ecomm e-mysql" style="display: none">Instead of <code>COALESCE</code> or <code>NVL</code>, <code>IFNULL</code> can be used.</div> | ||
<div class="ecomm e-sqlserver" style="display: none">Instead of <code>COALESCE</code> or <code>NVL</code>, <code>IFNULL</code> can be used.</div> | <div class="ecomm e-sqlserver" style="display: none">Instead of <code>COALESCE</code> or <code>NVL</code>, <code>IFNULL</code> can be used.</div> | ||
</div> | </div> | ||
{{Hacks Ref}} | {{Hacks Ref}} | ||
Latest revision as of 15:01, 2 August 2012
Normally a string can be searched for across many columns using the OR function but this is not efficient as this could lead to errors while using
a CONCAT function ( || for oracle, + for sqlserver) could do the same task but can get rid of the risk of errors
DROP TABLE bedrooms
CREATE TABLE bedrooms( name VARCHAR(20), floorcolor VARCHAR(20), ceilingcolor VARCHAR(20), wallcolor VARCHAR(20)); INSERT INTO bedrooms VALUES ('Jim','RED','GREEN','YELLOW'); INSERT INTO bedrooms VALUES ('Bob','YELLOW','BLUE','BLACK'); INSERT INTO bedrooms VALUES ('Allan','BLUE','PINK','BLACK'); INSERT INTO bedrooms VALUES ('George','BLUE','GREEN','OAK');
SELECT name FROM bedrooms
WHERE floorcolor = 'YELLOW'
OR ceilingcolor = 'YELLOW'
OR wallcolor = 'YELLOW'
Using OR increases the chances for careless mistakes instead
CONCAT could be used to make the query more efficient.
To avoid problems make sure to add in separators and if a value can be null
make sure to use it is wrapped in COALESCE or NVL for example:
COALESCE(floorcolor,' ').
SELECT name FROM bedrooms WHERE ':' || floorcolor || ':' || ceilingcolor || ':' || wallcolor || ':' LIKE '%:YELLOW:%'
SELECT name FROM bedrooms WHERE ':' + floorcolor + ':' + ceilingcolor + ':' + wallcolor + ':' LIKE '%:YELLOW:%'
SELECT name FROM bedrooms WHERE CONCAT (':',floorcolor,':',ceilingcolor,':',wallcolor,':') LIKE '%:YELLOW:%'
Hack 10 Converting subqueries into joins
Hack 11 Converting aggregate subqueries into joins
Hack 16 Search for a String across columns
Hack 24 Multiply Across a Result Set
Hack 25.5 Splitting and combining columns
Hack 26 Include the rows your JOIN forgot
Hack 30 Calculate the maximum/minimum of two fields
Hack 33 Get values and subtotals in one shot
Hack 50 Combine tables containing different data
Hack 51/52 Display rows as columns
Hack 55 Import Someone Else's Data
Hack 62 Issue Queries Without Using a Table
Hack 63 Generate rows without tables
Hack 72 Extract a subset of the results
Hack 78 Break it down by Range
Hack 88 Test two values from a subquery
