我想在sqlite数据库中删除或添加列
我正在使用以下查询删除列。
ALTER TABLE TABLENAME DROP COLUMN COLUMNNAME
但它会产生错误
System.Data.SQLite.SQLiteException: SQLite error
near "DROP": syntax error
当前回答
有一段时间不直接支持这一点，您需要遵循以下四个步骤:(1)创建一个temporary_table，(2)复制数据，(3)删除旧表，然后(4)重命名temporary_table。
但是现在支持这些特性，您所需要做的就是升级SQLite。
3.35.0 from 2021-03-12添加ALTER TABLE DROP COLUMN 3.25.0 from 2018-09-15新增ALTER TABLE RENAME COLUMN 3.2.0在2005-03-21添加了ALTER TABLE ADD COLUMN
请注意，仍然有一些边缘情况下，这些可能不起作用，例如，您不能删除主键列。有关详细信息，请参阅文档。当这些ALTER TABLE…COLUMN语句不起作用时，您可以退回到四步过程。
顺便说一下，文档中的四步流程实际上是十二步流程。但其中四个步骤非常重要，很容易出错，在这些文档中特别指出。
其他回答
我已经改进了user2638929回答，现在它可以保留列类型，主键，默认值等。
public static void dropColumns(SQLiteDatabase database, String tableName, Collection<String> columnsToRemove){
List<String> columnNames = new ArrayList<>();
List<String> columnNamesWithType = new ArrayList<>();
List<String> primaryKeys = new ArrayList<>();
String query = "pragma table_info(" + tableName + ");";
Cursor cursor = database.rawQuery(query,null);
while (cursor.moveToNext()){
String columnName = cursor.getString(cursor.getColumnIndex("name"));
if (columnsToRemove.contains(columnName)){
continue;
}
String columnType = cursor.getString(cursor.getColumnIndex("type"));
boolean isNotNull = cursor.getInt(cursor.getColumnIndex("notnull")) == 1;
boolean isPk = cursor.getInt(cursor.getColumnIndex("pk")) == 1;
columnNames.add(columnName);
String tmp = "`" + columnName + "` " + columnType + " ";
if (isNotNull){
tmp += " NOT NULL ";
}
int defaultValueType = cursor.getType(cursor.getColumnIndex("dflt_value"));
if (defaultValueType == Cursor.FIELD_TYPE_STRING){
tmp += " DEFAULT " + "\"" + cursor.getString(cursor.getColumnIndex("dflt_value")) + "\" ";
}else if(defaultValueType == Cursor.FIELD_TYPE_INTEGER){
tmp += " DEFAULT " + cursor.getInt(cursor.getColumnIndex("dflt_value")) + " ";
}else if (defaultValueType == Cursor.FIELD_TYPE_FLOAT){
tmp += " DEFAULT " + cursor.getFloat(cursor.getColumnIndex("dflt_value")) + " ";
}
columnNamesWithType.add(tmp);
if (isPk){
primaryKeys.add("`" + columnName + "`");
}
}
cursor.close();
String columnNamesSeparated = TextUtils.join(", ", columnNames);
if (primaryKeys.size() > 0){
columnNamesWithType.add("PRIMARY KEY("+ TextUtils.join(", ", primaryKeys) +")");
}
String columnNamesWithTypeSeparated = TextUtils.join(", ", columnNamesWithType);
database.beginTransaction();
try {
database.execSQL("ALTER TABLE " + tableName + " RENAME TO " + tableName + "_old;");
database.execSQL("CREATE TABLE " + tableName + " (" + columnNamesWithTypeSeparated + ");");
database.execSQL("INSERT INTO " + tableName + " (" + columnNamesSeparated + ") SELECT "
+ columnNamesSeparated + " FROM " + tableName + "_old;");
database.execSQL("DROP TABLE " + tableName + "_old;");
database.setTransactionSuccessful();
}finally {
database.endTransaction();
}
}
PS:这里我使用的是android.arch.persistence.db。支持sqlitedatabase，但你可以很容易地修改它使用android.database.sqlite.SQLiteDatabase
正如其他人指出的那样，sqlite的ALTER TABLE语句不支持DROP COLUMN，并且标准的做法是不保留约束和索引。
下面是一些python代码，在维护所有关键约束和索引的同时，可以通用地执行此操作。
请在使用之前备份您的数据库!这个函数依赖于修改原始的CREATE TABLE语句，可能有点不安全——例如，如果标识符包含嵌入的逗号或圆括号，它就会出错。
如果有人愿意提供一种更好的解析SQL的方法，那就太好了!
我发现了一个更好的方法来解析使用开源sqlparse包。如果有任何兴趣，我会张贴在这里，只要留下评论要求它…
import re
import random
def DROP_COLUMN(db, table, column):
columns = [ c[1] for c in db.execute("PRAGMA table_info(%s)" % table) ]
columns = [ c for c in columns if c != column ]
sql = db.execute("SELECT sql from sqlite_master where name = '%s'"
% table).fetchone()[0]
sql = format(sql)
lines = sql.splitlines()
findcol = r'\b%s\b' % column
keeplines = [ line for line in lines if not re.search(findcol, line) ]
create = '\n'.join(keeplines)
create = re.sub(r',(\s*\))', r'\1', create)
temp = 'tmp%d' % random.randint(1e8, 1e9)
db.execute("ALTER TABLE %(old)s RENAME TO %(new)s" % {
'old': table, 'new': temp })
db.execute(create)
db.execute("""
INSERT INTO %(new)s ( %(columns)s )
SELECT %(columns)s FROM %(old)s
""" % {
'old': temp,
'new': table,
'columns': ', '.join(columns)
})
db.execute("DROP TABLE %s" % temp)
def format(sql):
sql = sql.replace(",", ",\n")
sql = sql.replace("(", "(\n")
sql = sql.replace(")", "\n)")
return sql
Kotlin解决方案，基于这里，还要:
确保临时表不存在 修复了检查默认值的类型，因为当它是Integer时返回String类型(此处报告了此问题)。 避免在希望删除的列不存在时执行任何操作。
object DbUtil {
/** https://stackoverflow.com/a/51587449/878126 */
@JvmStatic
fun dropColumns(database: SQLiteDatabase, tableName: String,
columnsToRemove: Collection<String>) {
val columnNames: MutableList<String> = ArrayList()
val columnNamesWithType: MutableList<String> = ArrayList()
val primaryKeys: MutableList<String> = ArrayList()
val query = "pragma table_info($tableName);"
val cursor = database.rawQuery(query, null)
val columnDefaultIndex = cursor.getColumnIndex("dflt_value")
val columnNameIndex = cursor.getColumnIndex("name")
val columnTypeIndex = cursor.getColumnIndex("type")
val columnNotNullIndex = cursor.getColumnIndex("notnull")
val columnPrimaryKeyIndex = cursor.getColumnIndex("pk")
val sb = StringBuilder()
var foundColumnsToRemove = false
while (cursor.moveToNext()) {
val columnName = cursor.getString(columnNameIndex)
if (columnsToRemove.contains(columnName)) {
foundColumnsToRemove = true
continue
}
val columnType = cursor.getString(columnTypeIndex)
val isNotNull = cursor.getInt(columnNotNullIndex) == 1
val isPrimaryKey = cursor.getInt(columnPrimaryKeyIndex) == 1
columnNames.add(columnName)
sb.clear()
sb.append("`$columnName` $columnType ")
if (isNotNull)
sb.append(" NOT NULL ")
if (cursor.getType(columnDefaultIndex) != Cursor.FIELD_TYPE_NULL) {
//has default value
when (columnType.uppercase()) {
"INTEGER" -> sb.append(" DEFAULT ${cursor.getInt(columnDefaultIndex)} ")
"TEXT" -> sb.append(" DEFAULT \"${cursor.getString(columnDefaultIndex)}\" ")
"REAL" -> sb.append(" DEFAULT ${cursor.getFloat(columnDefaultIndex)} ")
}
}
columnNamesWithType.add(sb.toString())
if (isPrimaryKey)
primaryKeys.add("`$columnName`")
}
cursor.close()
if (!foundColumnsToRemove)
return
val columnNamesSeparated = TextUtils.join(", ", columnNames)
if (primaryKeys.size > 0)
columnNamesWithType.add("PRIMARY KEY(${TextUtils.join(", ", primaryKeys)})")
val columnNamesWithTypeSeparated = TextUtils.join(", ", columnNamesWithType)
database.beginTransaction()
try {
var newTempTableName: String
var counter = 0
while (true) {
newTempTableName = "${tableName}_old_$counter"
if (!isTableExists(database, newTempTableName))
break
++counter
}
database.execSQL("ALTER TABLE $tableName RENAME TO $newTempTableName;")
database.execSQL("CREATE TABLE $tableName ($columnNamesWithTypeSeparated);")
database.execSQL(
"INSERT INTO $tableName ($columnNamesSeparated) SELECT $columnNamesSeparated FROM $newTempTableName;")
database.execSQL("DROP TABLE ${newTempTableName};")
database.setTransactionSuccessful()
} finally {
database.endTransaction()
}
}
@JvmStatic
fun isTableExists(database: SQLiteDatabase, tableName: String): Boolean {
database.rawQuery(
"select DISTINCT tbl_name from sqlite_master where tbl_name = '$tableName'", null)
?.use {
return it.count > 0
} ?: return false
}
}
public void DeleteColFromTable(String DbName, String TableName, String ColName){
SQLiteDatabase db = openOrCreateDatabase(""+DbName+"", Context.MODE_PRIVATE, null);
db.execSQL("CREATE TABLE IF NOT EXISTS "+TableName+"(1x00dff);");
Cursor c = db.rawQuery("PRAGMA table_info("+TableName+")", null);
if (c.getCount() == 0) {
} else {
String columns1 = "";
String columns2 = "";
while (c.moveToNext()) {
if (c.getString(1).equals(ColName)) {
} else {
columns1 = columns1 + ", " + c.getString(1) + " " + c.getString(2);
columns2 = columns2 + ", " + c.getString(1);
}
if (c.isLast()) {
db.execSQL("CREATE TABLE IF NOT EXISTS DataBackup (" + columns1 + ");");
db.execSQL("INSERT INTO DataBackup SELECT " + columns2 + " FROM "+TableName+";");
db.execSQL("DROP TABLE "+TableName+"");
db.execSQL("ALTER TABLE DataBackup RENAME TO "+TableName+";");
}
}
}
}
只需要调用一个方法
DeleteColFromTable("Database name","Table name","Col name which want to delete");
基于http://www.sqlite.org/faq.html#q11上的信息在Python中实现。
import sqlite3 as db
import random
import string
QUERY_TEMPLATE_GET_COLUMNS = "PRAGMA table_info(@table_name)"
QUERY_TEMPLATE_DROP_COLUMN = """
BEGIN TRANSACTION;
CREATE TEMPORARY TABLE @tmp_table(@columns_to_keep);
INSERT INTO @tmp_table SELECT @columns_to_keep FROM @table_name;
DROP TABLE @table_name;
CREATE TABLE @table_name(@columns_to_keep);
INSERT INTO @table_name SELECT @columns_to_keep FROM @tmp_table;
DROP TABLE @tmp_table;
COMMIT;
"""
def drop_column(db_file, table_name, column_name):
con = db.connect(db_file)
QUERY_GET_COLUMNS = QUERY_TEMPLATE_GET_COLUMNS.replace("@table_name", table_name)
query_res = con.execute(QUERY_GET_COLUMNS).fetchall()
columns_list_to_keep = [i[1] for i in query_res if i[1] != column_name]
columns_to_keep = ",".join(columns_list_to_keep)
tmp_table = "tmp_%s" % "".join(random.sample(string.ascii_lowercase, 10))
QUERY_DROP_COLUMN = QUERY_TEMPLATE_DROP_COLUMN.replace("@table_name", table_name)\
.replace("@tmp_table", tmp_table).replace("@columns_to_keep", columns_to_keep)
con.executescript(QUERY_DROP_COLUMN)
con.close()
drop_column(DB_FILE, TABLE_NAME, COLUMN_NAME)
这个脚本首先创建随机的临时表，并只插入必要列的数据，除了将要删除的列。然后根据临时表恢复原表，删除临时表。
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