我想将我的 iPhone 应用程序迁移到新的数据库版本。由于我没有保存某些版本,因此我需要检查某些列名是否存在。
此 Stackoverflow entry 建议进行选择
SELECT sql FROM sqlite_master
WHERE tbl_name = 'table_name' AND type = 'table'
并解析结果。
这是常见的方式吗?备择方案?
PRAGMA table_info(table_name);
将为您提供所有列名的列表。
如果您有 sqlite 数据库,请使用 sqlite3 命令行程序和以下命令:
列出数据库中的所有表:
.tables
要显示给定 tablename
的架构:
.schema tablename
PRAGMA table_info(table_name);
更容易记住
如果你这样做
.headers ON
你会得到想要的结果。
.sqliterc
file。
PRAGMA
方法和 .schema
方法都不适用于我。但是这个工作得很好。
.headers on
和 .mode columns
将打开列名并对齐所有内容
只是为了像我这样的超级菜鸟想知道人们的意思是什么
PRAGMA table_info('table_name')
您想使用它作为您的准备语句,如下所示。这样做会选择一个看起来像这样的表,除了填充与您的表有关的值。
cid name type notnull dflt_value pk
---------- ---------- ---------- ---------- ---------- ----------
0 id integer 99 1
1 name 0 0
其中 id 和 name 是列的实际名称。因此,要获得该值,您需要使用以下方法选择列名:
//returns the name
sqlite3_column_text(stmt, 1);
//returns the type
sqlite3_column_text(stmt, 2);
这将返回当前行的列名。要全部获取它们或找到您想要的,您需要遍历所有行。最简单的方法是采用以下方式。
//where rc is an int variable if wondering :/
rc = sqlite3_prepare_v2(dbPointer, "pragma table_info ('your table name goes here')", -1, &stmt, NULL);
if (rc==SQLITE_OK)
{
//will continue to go down the rows (columns in your table) till there are no more
while(sqlite3_step(stmt) == SQLITE_ROW)
{
sprintf(colName, "%s", sqlite3_column_text(stmt, 1));
//do something with colName because it contains the column's name
}
}
sqlite3
(或为您命名的任何名称)进入 sqlite CLI,然后输入该文本。无需为此编写大量代码:)
sqlite3
。此外,@birdbuster,它有助于指定您正在使用的语言和库。在我看来,它看起来像 C++(来自 sprintf
函数)。澄清一下是有帮助的,因为 OP 问题与语言无关。
如果您希望查询的输出包含列名并正确对齐为列,请在 sqlite3
中使用以下命令:
.headers on
.mode column
你会得到如下输出:
sqlite> .headers on
sqlite> .mode column
sqlite> select * from mytable;
id foo bar
---------- ---------- ----------
1 val1 val2
2 val3 val4
获取此处未提及的列名列表的另一种方法是跨平台且不依赖于 sqlite3.exe shell,是从 PRAGMA_TABLE_INFO() 表值函数中进行选择。
SELECT name FROM PRAGMA_TABLE_INFO('your_table');
name
tbl_name
rootpage
sql
您可以通过查询来检查某个列是否存在:
SELECT 1 FROM PRAGMA_TABLE_INFO('your_table') WHERE name='column1';
1
如果您不想从 sqlite_master 或 pragma table_info 解析 select sql 的结果,这就是您使用的。
请注意,此功能是实验性的,已在 SQLite 版本 3.16.0 (2017-01-02) 中添加。
参考:
https://www.sqlite.org/pragma.html#pragfunc
要获取列列表,您可以简单地使用:
.schema tablename
我知道这是一个旧线程,但最近我需要它并找到了一个简洁的方法:
SELECT c.name FROM pragma_table_info('your_table_name') c;
where t.name = 'table';
当您运行 sqlite3
cli 时,输入:
sqlite3 -header
也会给出想要的结果
.schema table_name
这将列出数据库中表的列名。
希望这会有所帮助!!!
如果您正在搜索任何特定列,则可以使用 Like 语句
前任:
SELECT * FROM sqlite_master where sql like('%LAST%')
为了获取列信息,您可以使用以下代码段:
String sql = "select * from "+oTablename+" LIMIT 0";
Statement statement = connection.createStatement();
ResultSet rs = statement.executeQuery(sql);
ResultSetMetaData mrs = rs.getMetaData();
for(int i = 1; i <= mrs.getColumnCount(); i++)
{
Object row[] = new Object[3];
row[0] = mrs.getColumnLabel(i);
row[1] = mrs.getColumnTypeName(i);
row[2] = mrs.getPrecision(i);
}
//JUST little bit modified the answer of giuseppe which returns array of table columns
+(NSMutableArray*)tableInfo:(NSString *)table{
sqlite3_stmt *sqlStatement;
NSMutableArray *result = [NSMutableArray array];
const char *sql = [[NSString stringWithFormat:@"PRAGMA table_info('%@')",table] UTF8String];
if(sqlite3_prepare(md.database, sql, -1, &sqlStatement, NULL) != SQLITE_OK)
{
NSLog(@"Problem with prepare statement tableInfo %@",
[NSString stringWithUTF8String:(const char *)sqlite3_errmsg(md.database)]);
}
while (sqlite3_step(sqlStatement)==SQLITE_ROW)
{
[result addObject:
[NSString stringWithUTF8String:(char*)sqlite3_column_text(sqlStatement, 1)]];
}
return result;
}
当你在桌子里时,sqlite 控制台中的 .schema 对我来说看起来像这样......
sqlite>.schema
CREATE TABLE players(
id integer primary key,
Name varchar(255),
Number INT,
Team varchar(255)
function getDetails(){
var data = [];
dBase.executeSql("PRAGMA table_info('table_name') ", [], function(rsp){
if(rsp.rows.length > 0){
for(var i=0; i<rsp.rows.length; i++){
var o = {
name: rsp.rows.item(i).name,
type: rsp.rows.item(i).type
}
data.push(o);
}
}
alert(rsp.rows.item(0).name);
},function(error){
alert(JSON.stringify(error));
});
}
这是一个老问题,但这里有一个替代答案,它检索 SQLite 数据库中的所有列,每列的关联表的名称:
WITH tables AS (SELECT name tableName, sql
FROM sqlite_master WHERE type = 'table' AND tableName NOT LIKE 'sqlite_%')
SELECT fields.name, fields.type, tableName
FROM tables CROSS JOIN pragma_table_info(tables.tableName) fields
这将返回这种类型的结果:
{
"name": "id",
"type": "integer",
"tableName": "examples"
}, {
"name": "content",
"type": "text",
"tableName": "examples"
}
对于包含标识符和字符串内容的简单表。
-(NSMutableDictionary*)tableInfo:(NSString *)table
{
sqlite3_stmt *sqlStatement;
NSMutableDictionary *result = [[NSMutableDictionary alloc] init];
const char *sql = [[NSString stringWithFormat:@"pragma table_info('%s')",[table UTF8String]] UTF8String];
if(sqlite3_prepare(db, sql, -1, &sqlStatement, NULL) != SQLITE_OK)
{
NSLog(@"Problem with prepare statement tableInfo %@",[NSString stringWithUTF8String:(const char *)sqlite3_errmsg(db)]);
}
while (sqlite3_step(sqlStatement)==SQLITE_ROW)
{
[result setObject:@"" forKey:[NSString stringWithUTF8String:(char*)sqlite3_column_text(sqlStatement, 1)]];
}
return result;
}
我知道为时已晚,但这将对其他人有所帮助。
要查找表的列名,您应该执行 select * from tbl_name
,您将在 sqlite3_stmt *
中获得结果。并检查列迭代总提取列。请参考以下代码。
// sqlite3_stmt *statement ;
int totalColumn = sqlite3_column_count(statement);
for (int iterator = 0; iterator<totalColumn; iterator++) {
NSLog(@"%s", sqlite3_column_name(statement, iterator));
}
这将打印结果集的所有列名。
下面的这个命令设置列名:
.header on
然后,它如下所示:
sqlite> select * from user;
id|first_name|last_name|age
1|Steve|Jobs|56
2|Bill|Gates|66
3|Mark|Zuckerberg|38
下面的这个命令会取消设置列名:
.header off
然后,它如下所示:
sqlite> select * from user;
1|Steve|Jobs|56
2|Bill|Gates|66
3|Mark|Zuckerberg|38
这些命令显示命令“.header”的详细信息:
.help .header
或者:
.help header
然后,它如下所示:
sqlite> .help .header
.headers on|off Turn display of headers on or off
此外,下面的这个命令设置输出模式“box”:
.mode box
然后,它如下所示:
sqlite> select * from user;
┌────┬────────────┬────────────┬─────┐
│ id │ first_name │ last_name │ age │
├────┼────────────┼────────────┼─────┤
│ 1 │ Steve │ Jobs │ 56 │
│ 2 │ Bill │ Gates │ 66 │
│ 3 │ Mark │ Zuckerberg │ 38 │
└────┴────────────┴────────────┴─────┘
并且,下面的这个命令设置了输出模式“table”:
.mode table
然后,它如下所示:
sqlite> select * from user;
+----+------------+------------+-----+
| id | first_name | last_name | age |
+----+------------+------------+-----+
| 1 | Steve | Jobs | 56 |
| 2 | Bill | Gates | 66 |
| 3 | Mark | Zuckerberg | 38 |
+----+------------+------------+-----+
这些命令显示了命令“.mode”的详细信息:
.help .mode
或者:
.help mode
然后,它如下所示:
sqlite> .help .mode
.import FILE TABLE Import data from FILE into TABLE
Options:
--ascii Use \037 and \036 as column and row separators
--csv Use , and \n as column and row separators
--skip N Skip the first N rows of input
--schema S Target table to be S.TABLE
-v "Verbose" - increase auxiliary output
Notes:
* If TABLE does not exist, it is created. The first row of input
determines the column names.
* If neither --csv or --ascii are used, the input mode is derived
from the ".mode" output mode
* If FILE begins with "|" then it is a command that generates the
input text.
.mode MODE ?OPTIONS? Set output mode
MODE is one of:
ascii Columns/rows delimited by 0x1F and 0x1E
box Tables using unicode box-drawing characters
csv Comma-separated values
column Output in columns. (See .width)
html HTML <table> code
insert SQL insert statements for TABLE
json Results in a JSON array
line One value per line
list Values delimited by "|"
markdown Markdown table format
qbox Shorthand for "box --width 60 --quote"
quote Escape answers as for SQL
table ASCII-art table
tabs Tab-separated values
tcl TCL list elements
OPTIONS: (for columnar modes or insert mode):
--wrap N Wrap output lines to no longer than N characters
--wordwrap B Wrap or not at word boundaries per B (on/off)
--ww Shorthand for "--wordwrap 1"
--quote Quote output text as SQL literals
--noquote Do not quote output text
TABLE The name of SQL table used for "insert" mode
//Called when application is started. It works on Droidscript, it is tested
function OnStart()
{
//Create a layout with objects vertically centered.
lay = app.CreateLayout( "linear", "VCenter,FillXY" );
//Create a text label and add it to layout.
txt = app.CreateText( "", 0.9, 0.4, "multiline" )
lay.AddChild( txt );
app.AddLayout(lay);
db = app.OpenDatabase( "MyData" )
//Create a table (if it does not exist already).
db.ExecuteSql( "drop table if exists test_table" )
db.ExecuteSql( "CREATE TABLE IF NOT EXISTS test_table " +
"(id integer primary key, data text, num integer)",[],null, OnError )
db.ExecuteSql( "insert into test_table values (1,'data10',100),
(2,'data20',200),(3,'data30',300)")
//Get all the table rows.
DisplayAllRows("SELECT * FROM test_table");
DisplayAllRows("select *, id+100 as idplus, 'hahaha' as blabla from
test_table order by id desc;")
}
//function to display all records
function DisplayAllRows(sqlstring) // <-- can you use for any table not need to
// know column names, just use a *
// example:
{
//Use all rows what is in ExecuteSql (try any, it will works fine)
db.ExecuteSql( sqlstring, [], OnResult, OnError )
}
//Callback to show query results in debug.
function OnResult( res )
{
var len = res.rows.length;
var s = txt.GetText();
// ***********************************************************************
// This is the answer how to read column names from table:
for(var ColumnNames in res.rows.item(0)) s += " [ "+ ColumnNames +" ] "; // "[" & "]" optional, i use only in this demo
// ***********************************************************************
//app.Alert("Here is all Column names what Select from your table:\n"+s);
s+="\n";
for(var i = 0; i < len; i++ )
{
var rows = res.rows.item(i)
for (var item in rows)
{
s += " " + rows[item] + " ";
}
s+="\n\n";
}
//app.Alert(s);
txt.SetText( s )
}
//Callback to show errors.
function OnError( msg )
{
app.Alert( "Error: " + msg )
}
如果您使用的是 SQLite3,则不支持 INFORMATION_SCHEMA。请改用 PRAGMA table_info。这将返回有关表的 6 行信息。要获取列名 (row2),请使用如下的 for 循环
cur.execute("PRAGMA table_info(table_name)") # fetches the 6 rows of data
records = cur.fetchall()
print(records)
for row in records:
print("Columns: ", row[1])
我能够通过使用一个 sql 查询来检索具有相应列的表名,但列输出是逗号分隔的。我希望它可以帮助某人
SELECT tbl_name, (SELECT GROUP_CONCAT(name, ',') FROM PRAGMA_TABLE_INFO(tbl_name)) as columns FROM sqlite_schema WHERE type = 'table';
在 Python 中使用 sqlite3
Top answer PRAGMA table_info()
返回一个元组列表,可能不适合进一步处理,例如:
[(0, 'id', 'INTEGER', 0, None, 0),
(1, 'name', 'TEXT', 0, None, 0),
(2, 'age', 'INTEGER', 0, None, 0),
(3, 'profession', 'TEXT', 0, None, 0)]
在 Python 中使用 sqlite3 时,只需在末尾添加一个列表推导即可过滤掉不需要的信息。
import sqlite3 as sq
def col_names(t_name):
with sq.connect('file:{}.sqlite?mode=ro'.format(t_name),uri=True) as conn:
cursor = conn.cursor()
cursor.execute("PRAGMA table_info({}) ".format(t_name))
data = cursor.fetchall()
return [i[1] for i in data]
col_names("your_table_name")
结果
["id","name","age","profession"]
免责声明:请勿在生产中使用,因为此代码段可能会受到 SQL 注入的影响!
获取表和列的列表作为视图:
CREATE VIEW Table_Columns AS
SELECT m.tbl_name AS TableView_Name, m.type AS TableView, cid+1 AS Column, p.*
FROM sqlite_master m, Pragma_Table_Info(m.tbl_name) p
WHERE m.type IN ('table', 'view') AND
( m.tbl_name = 'mypeople' OR m.tbl_name LIKE 'US_%') -- filter tables
ORDER BY m.tbl_name;
create temporary table TmpCols (cid integer, name text, type text, nn bit, dflt_value, pk bit); .mode insert TmpCols .output cols PRAGMA TABLE_INFO('yourtable'); .read cols .mode csv .output stdout
db.rawQuery("PRAGMA table_info(" + tablename + ")", null);
select * from pragma_table_info('tblName') as tblInfo;