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SQL update query using joins
I have to update a field with a value which is returned by a join of 3 tables.
11 Answers
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postgresql COUNT(DISTINCT …) very slow
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You can use this:
SELECT COUNT(*) FROM (SELECT DISTINCT column_name FROM table_name) AS temp;
This is much faster than:
COUNT(DISTINCT column_name)
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SQLite string contains other string query
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Using LIKE:
SELECT *
FROM TABLE
WHERE column LIKE '%cats%' --case-insensitive
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Row count with PDO
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$sql = "SELECT count(*) FROM `table` WHERE foo = ?";
$result = $con->prepare($sql);
$result->execute([$bar]);
$number_of_rows = $result->fetchColumn();
Not the most elegant way to do it, plus it involves an extra query.
PDO has PDOStatemen...
SQL Server: Get data for only the past year
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This will have very bad performance on big tables, you query will loop over every record to evaluate the year value of the date, it would be better to use a date range
– Adriaan Davel
May 30 '12 at 15:43
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Is it possible to force Excel recognize UTF-8 CSV files automatically?
...nsion XLS you will get the correct result.
Content of UTF8 XLS file:
<table>
<tr><td>Colum1</td><td>Column2</td></tr>
<tr><td>Val1</td><td>Val2</td></tr>
<tr><td>Авиабилет</td><td>Tλλη...
Why should I use document based database instead of relational database?
...ds of applications or domains where the document based database is more suitable than the relational database?
7 Answers
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What is the difference between single and double quotes in SQL?
...stant or a date/time constant.
Double quotes delimit identifiers for e.g. table names or column names. This is generally only necessary when your identifier doesn't fit the rules for simple identifiers.
See also:
Do different databases use different name quote?
You can make MySQL use double-q...
Create an empty data.frame
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You could use read.table with an empty string for the input text as follows:
colClasses = c("Date", "character", "character")
col.names = c("Date", "File", "User")
df <- read.table(text = "",
colClasses = colClasses,
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Check with jquery if div has overflowing elements
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Works for most cases but won't cover up scenario with CSS tables (display table-cell, table-rwo, table) -
– Dmitry
Jul 1 '14 at 13:55
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