Following is the example of using the NULL value in SQLite while creating a table called STUDENT. The statement below returns 0 if the value is NULL.
Suppose you have an employee table containing. The SQLite IFNULL() function lets you to provide an alternative value if column value is NULL. It is not equivalent to empty string or zero. Generally, we can use NULL value while creating a table. Empty struct that can be used to fill in a query parameter as NULL. The NULL value is a data type that represents an unknown value. We will learn more about COALESCE function in later topics. The SQLite COALESCE function takes a list of values and returns the first non-NULL in the list. In SQLite we have a function called COALESCE to deal with NUL values. It will not count the column with a NULL value.įollowing is the truth table that shows how NULL value will react with Logical expressions i.e.
#Sqlite insert value nul how to
You can try it if main example won't work.In SQLite, it is important to note that how to count(*) and count(column) will work when they are handling NULL values.Ĭount(*) - It only count records regardless of any NULL values in a column and return the count.Ĭount(column) - It returns only the count of NOT-NULL values. Some sources tells that it's not enough and you should do something like this: with FDQuery1.ParamByName('name') do beginīut I can't confirm it. The SQLite Unique Constraint same as the Primary Key constraint except that Unique Constraint will accept single Null value but the Primary Key will not accept any Null values and we can create a number of Unique Constraints on the table but we can create only one Primary Key constraint on a table.
#Sqlite insert value nul code
It's not very good idea to execute query as String without parameters because this code is vulnerable to SQL injections. To achieve faster performance, follow these performance principles: Read fewer rows and columns: Optimize your queries to retrieve only the necessary data. Something like this: //Assign FDConnection1 to FDQuery1's Connection propertyį := 'INSERT OR REPLACE INTO Clients(Name,Notes) VALUES (:nameval,:notesval)' So, you have to use FDQuery to insert Null values, I suppose. Then call the Clear method: with FDQuery1.ParamByName('name') do begin
(I was expecting zero-value of Date or NULL value of Date, but NULL is different. To set the parameter value to Null, specify the parameter data type, Now, lets insert our very first article with only title information. Id := FDConnection1.ExecSQLScalar('SELECT FROM Clients VALUES id WHERE Name=:nameval',) įDConnection1.ExecSQL('UPDATE Clients SET Notes=:noteval WHERE id=:idval)',) Īccording to Embarcadero documentation ( here ): 0 So I have a Table in some sqlite3 DB that has the following structure: CREATE TABLE table00 ( id INTEGER PRIMARY KEY AUTOINCREMENT, value VARCHAR (100) UNIQUE NOT NULL ) I need to retrieve the id from this table to use it in some other query. If you supply such a column, then SQLite will be able to handle the situation where you have an empty. Like this: FDConnection1.ExecSQL('INSERT OR REPLACE INTO Clients(Name) VALUES (:nameval)',) your database that allows NULL values, if there is one. IfThen(someNote.isEmpty,'NULL','"'+Sanitize(someNote)+'"')+') ') Įdit2: Currently I see an option of creating new row with "INSERT OR REPLACE" and then use multiple UPDATEs in a row for each non-empty value. I've tried to overload it and specify and it didn't help.Ĭurrently I have to do it like this and I hate this messy code: FDConnection1.ExecSQL('INSERT OR REPLACE INTO Clients(Name,Notes) VALUES ('+ This raises an exception: could not convert variant of type (Null) into type (OleStr) This is how I tried it: var someName,someNote: string įDConnection1.ExecSQL('INSERT OR REPLACE INTO Clients(Name,Notes) VALUES (:nameval,:notesval)', Creating multiple variants of ExecSQL and nesting If statements isn't an option too - there are too many optional fields (18, to be exact). You need to provide more explanation of what you are trying to achieve: If you want to add a row with its Notes column set to Null, why not simply omit Notes from the list of fields, i.e. If value is empty, I would like to keep it at Null or default value. In my application values are provided by user input and functions, any many of them are optional.
I use Delphi 10, FireDAC and local SQLite DB.Įdit: Provided code is just an example.
#Sqlite insert value nul full
I don't see why would I want to have a DB full of empty strings in fields.
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