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How to convert an entire MySQL database characterset and collation to UTF-8?
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Use the ALTER DATABASE and ALTER TABLE commands.
ALTER DATABASE databasename CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci;
ALTER TABLE tablename CONVERT TO CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci;
Or if you're still on MySQL 5.5.2 or older wh...
What replaces cellpadding, cellspacing, valign, and align in HTML5 tables?
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/* cellpadding */
th, td { padding: 5px; }
/* cellspacing */
table { border-collapse: separate; border-spacing: 5px; } /* cellspacing="5" */
table { border-collapse: collapse; border-spacing: 0; } /* cellspacing="0" */
/* valign */
th, td { vertical-align: top; }
/* align (center) ...
Why does X[Y] join of data.tables not allow a full outer join, or a left join?
This is a bit of a philosophical question about data.table join syntax. I am finding more and more uses for data.tables, but still learning...
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ALTER TABLE without locking the table?
When doing an ALTER TABLE statement in MySQL, the whole table is read-locked (allowing concurrent reads, but prohibiting concurrent writes) for the duration of the statement. If it's a big table, INSERT or UPDATE statements could be blocked for a looooong time. Is there a way to do a "hot alter", li...
Explicit vs implicit SQL joins
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Personally I prefer the join syntax as its makes it clearer that the tables are joined and how they are joined. Try compare larger SQL queries where you selecting from 8 different tables and you have lots of filtering in the where. By using join syntax you separate out the parts where the tabl...
This Row already belongs to another table error when trying to add rows?
I have a DataTable which has some rows and I am using the select to filter the rows to get a collection of DataRows which I then loop through using foreach and add it to another DataTable, but it is giving me the error "This Row already belongs to another table". Here is the code:
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MySQL - Rows to Columns
...e of terms that I'll use for the rest of this post. This will be the base table:
select * from history;
+--------+----------+-----------+
| hostid | itemname | itemvalue |
+--------+----------+-----------+
| 1 | A | 10 |
| 1 | B | 3 |
| 2 | A | ...
How does a hash table work?
I'm looking for an explanation of how a hash table works - in plain English for a simpleton like me!
15 Answers
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Sql Server 'Saving changes is not permitted' error ► Prevent saving changes that require table re-cr
When I create a table in SQL Server and save it, if I try to edit the table design, like change a column type from int to real, I get this error:
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MySQL InnoDB not releasing disk space after deleting data rows from table
I have one MySQL table using the InnoDB storage engine; it contains about 2M data rows. When I deleted data rows from the table, it did not release allocated disk space. Nor did the size of the ibdata1 file reduce after running the optimize table command.
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