sql server - Ensuring no duplicates without unique constraint -

-

is possible ensure column doesn't contain duplicate values without using unique constraint (don't want go in reasons why being avoided) on column? in particular thinking of race conditions.

for sake of simplicity let's column in question of type nvarchar(50) (does type matter?)

it possible trigger, condition if not exists(... before insert. in fact unique constraint fastest.

another option create unique index on column , supposed faster trigger , condition.

if don't want add unique constraint existing table, can create additional table field nvarchar (50) , unique constraint on it. , insert value of field in new table before insert in main table in transaction (inside insert statement or in trigger).


Comments

Post a Comment

Popular posts from this blog

python - jinja2: TemplateSyntaxError: expected token ',', got 'string' -

-
i new jinja2 , having issue using python regular expression (re). in following code bold lines have error string in them. {% block content %} <div class="container"> {% l in lines %} {% if re.search(r"error", l) %} {# <<< throws error #} <b> {{ l }} </b> {% else %} {{ l }} <hr> {% endif %} {% endfor %} </div> {% endblock %} the re.search above throws following error: jinja2.exceptions.templatesyntaxerror templatesyntaxerror: expected token ',', got 'string' raw python code not supported in jinja2 template syntax. {% if re.search(r"error", l) %} replace line with {% if "error" in l %} can fix problem. if logical condition more complicated, should consider defining own custom filters (which can call python code) or complicated things in view layer. go check global namespace .
Read more

Qt4: how to send QString inside a struct via QSharedMemory -

-
i have struct struct control_data{ int column_number; qstring cell; }; i need send thread of qsharememory. read can't because qstring contains pointers inside. other ways? you have serialize struct byte array. can convert qstring const char* this: mystring.tostdstring().c_str(); but serializing qstring should work. the first step serialize struct qdatastream using qt, example here . then once struct can read , written can pass shared memory. a complete example of using qsharedmemory can found here . here relevant code: // first, test whether shared memory segment attached process. // if so, detach if (sharedmem.isattached()) { sharedmem.detach(); } ... qbuffer buffer; buffer.open( qbuffer::readwrite ); qdatastream out( &buffer ); out << youstruct; int size = buffer.size(); // size of int + size of qstring in bytes if ( !sharedmem.create( size ) ) { return; } // write shared memory sharedmem.lock(); char *to = (char*...
Read more

node.js - NodeJS remote terminal to Dropbear OpenWRT-Server -

-
i wandering whether there valid solution have remote terminal openwrt-box out of nodejs-app? connecting terminal works: ssh -i ~/.mykeys/id_rsa root@192.168.178.39 busybox v1.23.2 (2015-04-22 23:25:48 utc) built-in shell (ash) root@openwrt:~# the only interactive ssh solution nodejs doesn't interactive part described in readme.md following: var client = require('ssh2').client; var conn = new client(); conn.on('ready', function() { console.log('client :: ready'); conn.shell(function(err, stream) { if (err) throw err; stream.on('close', function() { console.log('stream :: close'); conn.end(); }).on('data', function(data) { console.log('stdout: ' + data); }).stderr.on('data', function(data) { console.log('stderr: ' + data); }); stream.end('ls -l\nexit\n'); }); }).connect({ host: '192.168.100.100', port: 22, username...
Read more