1.歸并重複項
原始mytable:
+------+-------+
| user | brand |
+------+-------+
| aa | 9 |
| bb | 4 |
| bb | 3 |
| cc | 9 |
輸出重複的次數:
+------+-------+----------+
| user | brand | count(*) |
| aa | 9 | 2 |
| bb | 3 | 1 |
| bb | 4 | 1 |
| cc | 9 | 1 |
儲存查詢結果,并且删除count<2的項:
将txt檔案導入資料庫
擷取行數
兩表的比對
表一:
+------+-------+-------+
| name | brand | other |
| fe | 49 | fe |
| wo | 99 | 4g |
| ef | 23 | ij |
| ig | 41 | fe |
表二
| name | brand |
| wo | 99 |
| ig | 40 |
| co | 34 |
| ef | 23 |
如何生成表3
| name | brand | other |buy|
| fe | 49 | fe |0 |
| wo | 99 | 4g |1 |
| ef | 23 | ij |0 |
| ig | 41 | fe |1 |
就是添加第四列,如果兩個表的name和brand同時相等,第四列buy的值得1,不等為0。求大神指點!
改名