Questions tagged [sql]
Structured Query Language (SQL) is a language for querying databases. Questions should include code examples, table structure, sample data, and a tag for the DBMS implementation (e.g. MySQL, PostgreSQL, Oracle, MS SQL Server, IBM DB2, etc.) being used. If your question relates solely to a specific DBMS (uses specific extensions/features), use that DBMS's tag instead. Answers to questions tagged with SQL should use ISO/IEC standard SQL.
47,251
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2769
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How can I prevent SQL injection in PHP?
If user input is inserted without modification into an SQL query, then the application becomes vulnerable to SQL injection, like in the following example:
$unsafe_variable = $_POST['user_input'];
...
794
votes
13
answers
320k
views
When to use single quotes, double quotes, and backticks in MySQL
I am trying to learn the best way to write queries. I also understand the importance of being consistent. Until now, I have randomly used single quotes, double quotes, and backticks without any real ...
- 27.5k
788
votes
4
answers
315k
views
SQL injection that gets around mysql_real_escape_string()
Is there an SQL injection possibility even when using mysql_real_escape_string() function?
Consider this sample situation. SQL is constructed in PHP like this:
$login = mysql_real_escape_string(...
- 82.8k
1664
votes
27
answers
2.1m
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SQL select only rows with max value on a column [duplicate]
I have this table for documents (simplified version here):
id
rev
content
1
1
...
2
1
...
1
2
...
1
3
...
How do I select one row per id and only the greatest rev?
With the above data, the ...
- 30k
388
votes
10
answers
484k
views
How can I return pivot table output in MySQL?
If I have a MySQL table looking something like this:
company_name
action
pagecount
Company A
PRINT
3
Company A
PRINT
2
Company A
PRINT
3
Company B
EMAIL
Company B
PRINT
2
Company B
PRINT
2
...
- 5,073
2022
votes
21
answers
1.8m
views
Select first row in each GROUP BY group?
I'd like to select the first row of each set of rows grouped with a GROUP BY.
Specifically, if I've got a purchases table that looks like this:
SELECT * FROM purchases;
My Output:
id
customer
total
...
- 153k
781
votes
19
answers
1.0m
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Get top 1 row of each group
I have a table which I want to get the latest entry for each group. Here's the table:
DocumentStatusLogs Table
ID
DocumentID
Status
DateCreated
2
1
S1
7/29/2011
3
1
S2
7/30/2011
6
1
S1
8/02/2011
...
- 29.9k
1336
votes
34
answers
1.2m
views
Retrieving the last record in each group - MySQL
There is a table messages that contains data as shown below:
Id Name Other_Columns
-------------------------
1 A A_data_1
2 A A_data_2
3 A A_data_3
4 B ...
- 27.3k
376
votes
12
answers
194k
views
Simulating group_concat MySQL function in Microsoft SQL Server 2005?
I'm trying to migrate a MySQL-based app over to Microsoft SQL Server 2005 (not by choice, but that's life).
In the original app, we used almost entirely ANSI-SQL compliant statements, with one ...
- 7,137
261
votes
9
answers
351k
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SQL Server dynamic PIVOT query?
I've been tasked with coming up with a means of translating the following data:
date category amount
1/1/2012 ABC 1000.00
2/1/2012 DEF 500.00
2/1/2012 ...
- 3,076
678
votes
36
answers
697k
views
Fetch the rows which have the Max value for a column for each distinct value of another column
Table:
UserId, Value, Date.
I want to get the UserId, Value for the max(Date) for each UserId. That is, the Value for each UserId that has the latest date.
How do I do this in SQL? (Preferably Oracle....
- 6,815
2426
votes
48
answers
3.3m
views
How to concatenate text from multiple rows into a single text string in SQL Server
Consider a database table holding names, with three rows:
Peter
Paul
Mary
Is there an easy way to turn this into a single string of Peter, Paul, Mary?
- 29.3k
106
votes
2
answers
8k
views
Cleansing User Passwords
How should I escape or cleanse user-provided passwords before I hash them and store them in my database?
When PHP developers consider hashing users' passwords for security purposes, they often tend ...
- 34.3k
5242
votes
27
answers
2.6m
views
What is the difference between "INNER JOIN" and "OUTER JOIN"?
Also, how do LEFT OUTER JOIN, RIGHT OUTER JOIN, and FULL OUTER JOIN fit in?
- 57.3k
83
votes
5
answers
458k
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How to include a PHP variable inside a MySQL statement
I'm trying to insert values in the contents table. It works fine if I do not have a PHP variable inside VALUES. When I put the variable $type inside VALUES then this doesn't work. What am I doing ...
- 10.2k