Question

让我们考虑以下SQlite示例表，其中存储了相同记录的多个版本：

CREATE TABLE MyRecords(
id LONG NOT NULL,
version LONG NOT NULL,
text TEXT,
PRIMARY KEY (id ASC, version ASC)
);

如何使用id列仅为每个不同的version值获取一行，以选择一个（如果表中保存了多个version值，则com.venework.app.venework E/AndroidRuntime: FATAL EXCEPTION: main Process: com.venework.app.venework, PID: 3556 java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.venework.app.venework/com.venework.app.venework.MainActivity}: java.lang.ClassNotFoundException: Didn't find class "com.venework.app.venework.MainActivity" on path: DexPathList[[zip file "/data/app/com.venework.app.venework-1/base.apk", zip file "/data/app/com.venework.app.venework-1/split_lib_slice_0_apk.apk", zip file "/data/app/com.venework.app.venework-1/split_lib_slice_1_apk.apk", zip file "/data/app/com.venework.app.venework-1/split_lib_slice_2_apk.apk", zip file "/data/app/com.venework.app.venework-1/split_lib_slice_3_apk.apk", zip file "/data/app/com.venework.app.venework-1/split_lib_slice_4_apk.apk", zip file "/data/app/com.venework.app.venework-1/split_lib_slice_5_apk.apk", zip file "/data/app/com.venework.app.venework-1/split_lib_slice_6_apk.apk", zip file "/data/app/com.venework.app.venework-1/split_lib_slice_7_apk.apk", zip file "/data/app/com.venework.app.venework-1/split_lib_slice_8_apk.apk", zip file "/data/app/com.venework.app.venework-1/split_lib_slice_9_apk.apk"], nativeLibraryDirectories=[/data/app/com.venework.app.venework-1/lib/arm64, /system/lib64, /vendor/lib64]] at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2844) at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3008) at android.app.ActivityThread.-wrap14(ActivityThread.java) at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1650) at android.os.Handler.dispatchMessage(Handler.java:102) at android.os.Looper.loop(Looper.java:154) at android.app.ActivityThread.main(ActivityThread.java:6688) at java.lang.reflect.Method.invoke(Native Method) at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1468) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1358) Caused by: java.lang.ClassNotFoundException: Didn't find class "com.venework.app.venework.MainActivity" on path: DexPathList[[zip file "/data/app/com.venework.app.venework-1/base.apk", zip file "/data/app/com.venework.app.venework-1/split_lib_slice_0_apk.apk", zip file "/data/app/com.venework.app.venework-1/split_lib_slice_1_apk.apk", zip file "/data/app/com.venework.app.venework-1/split_lib_slice_2_apk.apk", zip file "/data/app/com.venework.app.venework-1/split_lib_slice_3_apk.apk", zip file "/data/app/com.venework.app.venework-1/split_lib_slice_4_apk.apk", zip file "/data/app/com.venework.app.venework-1/split_lib_slice_5_apk.apk", zip file "/data/app/com.venework.app.venework-1/split_lib_slice_6_apk.apk", zip file "/data/app/com.venework.app.venework-1/split_lib_slice_7_apk.apk", zip file "/data/app/com.venework.app.venework-1/split_lib_slice_8_apk.apk", zip file "/data/app/com.venework.app.venework-1/split_lib_slice_9_apk.apk"],nativeLibraryDirectories=[/data/app/com.venework.app.venework-1/lib/arm64, /system/lib64, /vendor/lib64]] at dalvik.system.BaseDexClassLoader.findClass(BaseDexClassLoader.java:56)值最高？

Answer 1

尝试此查询：

SELECT *
FROM MyRecords r1
WHERE version = (SELECT MAX(version) FROM MyRecords r2 WHERE r1.id = r2.id)

Answer 2

您可以获取每个ID的最大版本，然后联接回来获取文本值

SELECT * 
  FROM (
    SELECT id, MAX(version) version
      FROM MyRecords
     GROUP BY id
) q JOIN MyRecords r
    ON q.id = r.id
   AND q.version = r.version

SQLFiddle

Answer 3

在SQLite 3.7.11或更高版本中，您只需use max() to select which row in a group to return：

SELECT id,
       MAX(version) AS version,
       text
FROM MyRecords
GROUP BY id;

如果Sqlite表中有多个字段，如何使用另一个字段来选择一个字段来区分行？

3 个答案: