You are well advised to choose a primary key that is not only unique, but also never changes during the lifetime of a table row. If you wonder why, search the internet for the thousands of questions asking for help with removing duplicate entries from a table. In a relational database, it is important to be able to identify an individual table row. Why auto-generated primary keys?Įvery table needs a primary key. In this article, I’ll explore the options and give recommendations. UPDATED : Sometimes customers ask me about the best choice for auto-generated primary keys. 0.Auto-generated auto-increment autoincrement identity columns postgresql primary key sequence uuid For example, the following expression will fail: Without the leading zero, the decimal can be mistaken for the operation character. To avoid unexpected errors, if your formula includes decimal values between -1 and 1, include a leading zero in your values. This formula performs a calculation to only allow the user to select dates between today and 14 days from today: You can also use calculations in constraints. This formula, when applied to a date field, prevents the user from entering a value earlier than today: In the constraint expression, the input for the question is always represented by a period.įor example, you can use the following formula to restrict the input of an integer field to positive numbers only: In your spreadsheet, the constraint expression is entered into the constraint field and informational text is entered into the constraint_message column of the survey worksheet. This can include a specific range of numbers, combinations of letters and numbers, or general pattern matching. Returns the value to the power specified.Īdding a constraint to a survey question restricts the accepted inputs for a response. Returns the arc tangent of the quotient of the values. Returns the base-ten logarithm of the value. Returns the natural logarithm of the value. Returns the natural exponent of the value. Returns the tangent of the value as an angle in radians. Returns the sine of the value as an angle in radians. Returns the cosine of the value as an angle in radians. The following mathematical functions are supported in Survey123: Returns the value from a specific question in a repeat record. Indexed-repeat(question, repeat, index number) Returns the index of the current record in a repeat. For more information, see Regular expressions. If(selected($')Ĭoncatenates all answers to a given question in a repeat, separated by the given separator.Īpplies a regular expression to the question's input. If the condition evaluates to true, returns a otherwise, returns b. Returns a false value if the expression would return true, and a true value if the expression would return false. Returns the substring beginning at the specified start and extends to the character at index end -1, where start and end begin at 0. String-length(question, expression, or value) This function also returns the number of attached files for image, audio, and file questions using the multiline appearance. Returns the number of selected answers for select_one and select_multiple questions. This function is used for select_one and select_multiple questions.
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