如果该行已经存在,我想更新该行的列,但如果它还不存在,那么我想插入一个新行。
相关问题
这种题型一般是SQL比较流行的
- UPDATE if exists else INSERT in SQL Server 2008
- Solutions for INSERT OR UPDATE on SQL Server
- Insert into a MySQL table or update if exists
尤其是 SQLite
- INSERT IF NOT EXISTS ELSE UPDATE?
- SQLite - UPSERT *not* INSERT or REPLACE
- SQLite UPSERT / UPDATE OR INSERT
- SQL: How to update or insert if doesn't exist?
寻找 SQLite.swift 实现
我试图通过使用 SQLite.swift 来节省开发时间用于 iOS 开发的包装器。我选择这个框架是因为它是 recommended on raywenderlich.com .我认为有一个更新或插入的语法示例会很有用。
策略
在this answer , Sam Saffron 说:
If you are generally doing updates I would ..
- Begin a transaction
- Do the update
- Check the rowcount
- If it is 0 do the insert
- Commit
If you are generally doing inserts I would
- Begin a transaction
- Try an insert
- Check for primary key violation error
- if we got an error do the update
- Commit
This way you avoid the select and you are transactionally sound on Sqlite.
这对我来说很有意义,所以在我下面的回答中,我提供了一个“通常进行更新”的示例。
最佳答案
在此示例中,用户词典存储在自定义键盘上键入的单词。如果该词已在词典中,则该词的频率计数递增 1。但如果该词之前未输入过,则会插入一个新行,默认频率为 1。
该表是使用以下架构创建的:
let userDictionary = Table("user_dictionary")
let wordId = Expression<Int64>("id")
let word = Expression<String>("word")
let frequency = Expression<Int64>("frequency")
// ...
let _ = try db.run( userDictionary.create(ifNotExists: true) {t in
t.column(wordId, primaryKey: true)
t.column(word, unique: true)
t.column(frequency, defaultValue: 1)
})
从问题中得出,这就是我们想要做的:
- Begin a transaction
- Do the update
- Check the rowcount
- If it is 0 do the insert
- Commit
代码如下所示。
let wordToUpdate = "hello"
// ...
// 1. wrap everything in a transaction
try db.transaction {
// scope the update statement (any row in the word column that equals "hello")
let filteredTable = userDictionary.filter(word == wordToUpdate)
// 2. try to update
if try db.run(filteredTable.update(frequency += 1)) > 0 { // 3. check the rowcount
print("updated word frequency")
} else { // update returned 0 because there was no match
// 4. insert the word
let rowid = try db.run(userDictionary.insert(word <- wordToUpdate))
print("inserted id: \(rowid)")
}
} // 5. if successful, transaction is commited
参见 SQLite.swift documentation寻求更多帮助。
关于ios - 如何使用 SQLite.swift 更新或插入,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/36790444/