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更換一個列的數據由於表:有區別與其他列在MySQL
ID || City_1 || City_2
=====================
1 || Beijing || null
2 || Stockholm || Paris
3 || Tokyo || Seoul
4 || Las Vegas || null
5 || Moscow || null
我想有區別地把所有非空列2列1,以便更換相應值,新列1看起來像這樣:
ID || City_1 || City_2
=====================
1 || Beijing || null
2 || Paris || Paris
3 || Seoul || Seoul
4 || Las Vegas || null
5 || Moscow || null
什麼是最好的語法呢?