Four of the most common errors in SQL Server connections

server| Error One. " SQL Server does not exist or access is denied "

This is the most complex, the cause of the error is more, need to check the aspect also more.

Generally speaking, there are several possibilities:

1,sql server name or IP address is spelled incorrectly
2, server-side network configuration is incorrect
3, the client network configuration is incorrect

To solve this problem, we generally follow the steps below to find out the cause of the error step by step.


============= First, check the network physical connection =============
Ping < server IP address/server name >

If ping < server IP address > is unsuccessful, indicating a problem with the physical connection, check
Hardware devices, such as network cards, HUB, routers and so on.
Another possibility is that the firewall software is installed between the client and the server, such as ISA Server.
The firewall software may block the response to ping,telnet, so when checking connectivity problems, we need to first
Temporarily shut down the firewall software, or open all blocked ports.

Ping < server name > failed if ping < server IP address > success
If there is a problem with name resolution, check to see if the DNS service is normal.
Sometimes the client and the server are not in the same LAN, and it is very likely that the server name will not be used directly
Called to identify the server, we can use the Hosts file for name resolution,
The specific methods are:

1. Use Notepad to open the Hosts file (usually located in C:\WINNT\system32\drivers\etc).
Add a corresponding record for the IP address and server name, such as:
172.168.10.24 MyServer

2. Or configure in SQL Server's client Network Utility, which is explained in detail later.


============= second, use the Telnet command to check the working status of the SQL Server server =============
Telnet < server IP address > 1433

If the command succeeds, you can see the cursor flashing in the upper-left corner after the screen flashes, indicating that SQL Server
The server is working properly and is listening for TCP/IP connections on port 1433
If the command returns an error message "Cannot open connection", the server side does not start the SQL Server service.
Either the TCP/IP protocol is not enabled on the server side or the server side does not have the default port on SQL Server
1433 on the monitor.


============= Next, we're going to check the server-side network configuration on the server,
Check to see if Named Pipes are enabled. TCP/IP protocol enabled et cetera =============
You can use SQL Server's own server network usage tools for checking.

Click: Program-Microsoft SQL Server-server network usage tool

After you open the tool, you can see in general what protocols are enabled by the server.
Generally speaking, we enable named Pipes and TCP/IP protocols.
Point in the TCP/IP protocol, select "Properties", we can check the SQK Server service default end
The setting of the port. In general, we use SQL Server's default 1433 port. If "Hide Server" is selected, it means
Taste the client is unable to see this server by enumerating the servers, which has a protective effect, but does not affect the connection.


============= Next we are going to the client to check the client's network configuration =============
We can also take advantage of SQL Server's own client network usage tools for checking,
The difference is that this is the client to run this tool.

Click: Program--Microsoft SQL Server--Client Network usage tool

After you open the tool, in the general item, you can see which protocols are enabled by the client.
In general, we also need to enable named Pipes and TCP/IP protocols.
Click the TCP/IP protocol and select Properties to check the client default connection port settings, which must be consistent with the server.

Click the Aliases tab, and you can also configure aliases for the server. The alias of the server is the name used to connect,
The server in the connection parameter is the true server name, which can be the same or different. Alias settings and usage hosts
There are similarities between the pieces.


Through the above several aspects of the inspection, basically can eliminate the first error.


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Two. " Unable to connect to server, user XXX login failed.

This error occurs because SQL Server uses the Windows only authentication method,
Therefore, users cannot connect using SQL Server's login account (such as SA). The workaround is as follows:

1. Use Enterprise Manager on the server side and select "Use Windows Authentication" to connect to SQL Server
In Enterprise Manager
--Right click on your server instance (that's the one with the green icon)
--Edit SQL Server Registration properties
--Select "Use Windows Authentication"

2. Expand SQL Server Group, right click on the name of the SQL Server server, select "Properties",
and select the Security tab
3. Under Authentication, select SQL Server and Windows.
4. Restart the SQL Server service.

In the above workaround, if you used the use Windows authentication connection in step 1th
SQL Server failed, fix the problem by modifying the registry:

1. Click "Start"-"Run", input regedit, enter Registry Editor
2. Expand the registry key sequentially and browse to the following registry keys:
[HKEY_LOCAL_MACHINE\Software\Microsoft\MSSqlserver\MSSqlServer]
3. Locate the name "LoginMode" on the right side of the screen, double-click to edit the double byte value
4. Change the original value from 1 to 2 and click "OK"
5. Close Registry Editor
6. Restart the SQL Server service.

At this point, the user can successfully use SA to create a new SQL Server registration in Enterprise Manager.
However, you still cannot use Windows Authentication mode to connect to SQL Server.
This is because there are two default logon accounts in SQL Server:
BUILTIN\Administrators
< machine name >\administrator was deleted.
To recover both accounts, you can use the following methods:

1. Open the Enterprise Manager, expand the server group, and then expand the server
2. Expand Security, right-click Login, and then click New Login
3. In the Name box, enter BUILTIN\Administrators
4. On the Server Roles tab, select System Administrators
5. Click "OK" to exit
6. Use the same method to add < machine name >\administrator login.

Description

The following registry key:
Hkey_local_machine\software\microsoft\mssqlserver\mssqlserver\loginmode
Determines what authentication mode SQL Server will take.
1. Means using Windows authentication mode
2. Indicates the use of mixed mode (Windows authentication and SQL Server authentication).


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Three. Prompt connection timeout

If you encounter a third error, it generally means that the client has found the server and can connect,
However, an error occurs because the connection time is greater than the allowed time.
This situation typically occurs when a user runs Enterprise Manager on the Internet to register another
A server on the Internet, and a slow connection, may cause the above timeout error. In some cases,
This error can also be caused by network problems on the LAN.

To resolve such an error, you can modify the client's connection timeout setting. By default, Enterprise Manager
The timeout setting for registering another SQL Server is 4 seconds, and the Query Analyzer is 15 seconds (which is why
There is a greater likelihood of errors occurring in Enterprise Manager).

The specific steps are:
Settings in Enterprise Manager:
1. In Enterprise Manager, select Tools on the menu, and then select options
2. In the SQL Server Enterprise Manager Properties window that pops up, click the Advanced tab
3. Enter a larger number, such as 20, in the box to the right of login timeout (seconds) under Connection settings.

Settings in Query Analyzer:
Tools--Options--connection--Sets the login timeout to a larger number


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Four. Most of the machines use TCP/IP to succeed, once I found that with named pipes can?

This is because, in the operating system after Windows 2000, MS to resolve SQL Server security issues will
TCP/IP is configured as the default connection protocol for SQL Server, and you can see it in Client Network Utility
The order of TCP/IP and name PIPE.

You can also:
[Hkey_local_machine\software\microsoft\mssqlserver\client\supersocketnetlib]
"Protocolorder" =hex (7): 74,00,63,00,70,00,00,00,00,00
See the default protocol.

2. How to change Named Pipes, TCP/IP, and how to write SQL statements in a program?
You can modify the location of the registry mentioned above:
Client side:
[Hkey_local_machine\software\microsoft\mssqlserver\client\supersocketnetlib]
"Protocolorder" =hex (7): 74,00,63,00,70,00,00,00,00,00

Server End:
[Hkey_local_machine\software\microsoft\mssqlserver\mssqlserver\supersocketnetlib]
"Protocolorder" =hex (7): 74,00,63,00,70,00,00,00,00,00