Cardinality/n_rows_in_table 应该尽可能==1,如果非常小,那用户考虑🙅不要建这个索引了。 因为mysql除聚簇索引外,普通索引是先查索引表,拿到查询结果去数据表中查询,如某一列的Cardinality很小,说明该列的值大部分都是重复的,在大部分都是重复的记录上添加索引,反而会变慢。(如在性别上创建索引,且极端情况下...
($res=$mysqli->query($q)){printf("Data inserted successfully...!\n");}//now display the table records$s="SELECT ID, Salary FROM EMPLOYEES";if($r=$mysqli->query($s)){printf("Table Records: Where Salary is decimal type! \n");while($row=$r->fetch_assoc()){printf(" ID: %d,...
ORM for TypeScript and JavaScript. Supports MySQL, PostgreSQL, MariaDB, SQLite, MS SQL Server, Oracle, SAP Hana, WebSQL databases. Works in NodeJS, Browser, Ionic, Cordova and Electron platforms. - typeorm/typeorm
Types of BLOB DatatypeMySQL provides four types of BLOB datatypes, each with varying maximum storage capacities. While they all serve the same purpose of storing binary data, such as images or files, they differ in the maximum size of objects they can accommodate. Here are the four BLOB ...
left and inner joins proper pagination for queries using joins query caching streaming raw results logging listeners and subscribers (hooks) supports closure table pattern schema declaration in models or separate configuration files connection configuration in json / xml / yml / env formats ...
latin1_swedish_ci i need to do case sensitive joins so i change all the tables involved in both databases to utf8mb4_cs_0900_as_cs now my queries are very slow ! the 'explain' shows that the indexes are being used. What can be the issue? i am using community version on Microsoft...
lateral views and joins. 1.minimal : SELECT STAR, FILTER on partition columns, LIMIT only 2.more : SELECT, FILTER, LIMIT only (+TABLESAMPLE, virtual columns) </description> </property> 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. ...
How to avoid cross joins how to avoid duplicates in CROSS JOIN Query How to avoid group by many columns How to avoid null values in PIVOT result set How to calculate campdate > todays date + 45 days in sql query How to calculate max value for decimal type how to calculate MTD, QT...
If you store values larger than the display width in an integer column that has theZEROFILLattribute, you may experience problems when MySQL generates temporary tables for some complicated joins. In these cases, MySQL assumes that the data values fit within the column display width. ...
How to avoid cross joins how to avoid duplicates in CROSS JOIN Query How to avoid group by many columns How to avoid null values in PIVOT result set How to calculate campdate > todays date + 45 days in sql query How to calculate max value for decimal type how to calculate MTD, QTD ...