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How to convert an entire MySQL database characterset and collation to UTF-8?

... 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...
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PostgreSQL Autoincrement

... Yes, SERIAL is the equivalent function. CREATE TABLE foo ( id SERIAL, bar varchar); INSERT INTO foo (bar) values ('blah'); INSERT INTO foo (bar) values ('blah'); SELECT * FROM foo; 1,blah 2,blah SERIAL is just a create table time macro around sequences. You can not ...
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MongoDB/NoSQL: Keeping Document Change History

...ific entities in a database. I've heard this called row versioning, a log table or a history table (I'm sure there are other names for it). There are a number of ways to approach it in an RDBMS--you can write all changes from all source tables to a single table (more of a log) or have a separate h...
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How to read the database table name of a Model instance?

Given a model's instance object, how can I get the database table's name? 1 Answer 1 ...
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How to remove unwanted space between rows and columns in table?

How do I remove the extra space between the rows and columns in the table. 14 Answers ...
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Update multiple rows in same query using PostgreSQL

... You can also use update ... from syntax and use a mapping table. If you want to update more than one column, it's much more generalizable: update test as t set column_a = c.column_a from (values ('123', 1), ('345', 2) ) as c(column_b, column_a) where c.column_b = t.c...
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MySQL “NOT IN” query

I wanted to run a simple query to throw up all the rows of Table1 where a principal column value is not present in a column in another table ( Table2 ). ...
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What does .SD stand for in data.table in R

... .SD stands for something like "Subset of Data.table". There's no significance to the initial ".", except that it makes it even more unlikely that there will be a clash with a user-defined column name. If this is your data.table: DT = data.table(x=rep(c("a","b","c"),eac...
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What integer hash function are good that accepts an integer hash key?

...hich is not uncommon), their hashes will be too. This is a problem in hash tables - you can end up with only 1/2 or 1/4 of the buckets being used. share | improve this answer | ...
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Specifying an Index (Non-Unique Key) Using JPA

...rsistence.Entity; import javax.persistence.Index; import javax.persistence.Table; @Entity @Table(name = "region", indexes = {@Index(name = "my_index_name", columnList="iso_code", unique = true), @Index(name = "my_index_name2", columnList="name", unique = false)}) publi...