SQL mysql sql SQLServer orclare 数据库优化 一点点优化 因为自己经常接触报表,数据量特别的大,查询的速度常常困扰自己,现在结合自己的一些平常的使用习惯,发发自己看法吧! 通常的查询速度影响元素: 1 lock 锁概念(nolock) (这也是查询慢最常见的问题,是程序设计的缺陷) 2 函数的应用(right、ltrim、rtrim,case ...
I converted a MySQL db to MsSQL db. And 190mb MySQL db become 700mb MsSQL db. Then shrink MsSQL db and now it is 500mb. What is the reason behind this huge difference? Why MsSQL db with same data has 2x more space in hdd?
Description: We run the following SQLs and we see inconsistent behaviors when some of column alias names, column names are the same: Output: mysql> drop table if exists t1; ate table t1(c1 int, c2 int); Query OK, 0 rows affected (0.01 sec) mysql> create table t1(c1 int, c2 int)...
But the result of the INSERT, see below, is exactly the same as the value inserted, so I think we can accept this. mysql> insert into t2 values (-2.2e-310); Query OK, 1 row affected (0.00 sec) -- This is an incorrect response. The INSERT should be rejected with SQLSTATE 22003....
* The current C-API (libmysql) and SQL functions will likewise remain available for backward compatibility. * The server MUST prevent in-use IDs from being re-issued. DEFERRED: As the aforementioned race condition is very unlikely to occur and the customer has confirmed they do not require ...
MariaDB and MySQL both support SQL to query the database and the tables. Hence, the coding standards are SQL-based standards in MariaDB and MySQL. As MariaDB is forked out of MySQL, you would find that MariaDB queries in almost all cases are exactly similar to MySQL queries. ...
Different RDBMSs have different dialects of SQL. Different versions of MySQL also support different features of SQL. In order to help users write SQL that is compatible across DBMSs and different versions of MySQL, there are special comments that look like comments to other DBMSs but as SQL ...
Check whether the sql_mode values of the source and destination databases are the same. If they are different, the migration may fail. You are advised to change them to t
在Sqoop往mysql导出数据的时候报了这个错误,一开始还以为是jar包没有打进去或者打错位置了,未解便上网查询。 1 2 Error reading from database: java.sql.SQLException: Streaming resultsetcom.mysql.jdbc.RowDataDynamic@27ce24aa is still active. No statements may be issued when any streaming result sets ...
I am using MySQL Connector/J 5.1.6, and I've got the following exception in my application: java.sql.SQLException: Connection is read-only. Queries leading to data modification are not allowed. at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:1055) ...